I think Arcteryx is hard to know in sizing... Seems much of the clothes are bulky in the torso for my liking. I have many products because I like the quality, quality is the same with Norrøna, but they are not bulky at all.
To answer somewhat I am the same size as you, wear Small in Alpha SV jacket(no problem layering), Small in Beta AR pant, Small in Covert cardigan, but medium in Venta vest and squamish hoody. These clothes are worn in alpine environment in Norway (also hunting), I use medium in running clothes from Arcteryx. So in conclusion I would wait for more answers from others before ordering, that is if you as me, do NOT like bulky clothing.

Regards from Norway

First, fit: You should fit well into a medium in most Arc'teryx gear. I'm your height, but a bit heavier, and I'm right at the top end of medium. The sleeves and body length are perfect.

This jacket will probably soak through in a downpour. It's designed to be more wind-resistant and warm in cool conditions. Although the DWR lets it shed moisture, I wouldn't take mine out in the rain.

Finally, it will take some effort to tear or wear out this fabric. It's pretty tough stuff.

Don't have a large here for cuff size, but it fit's pretty close to the wrist. I can put a light glove under the cuff, but not a really warm one; that would have to go over the top which works well because the jacket cuff is trim. There would be room to layer under the Gamma MX, with something that also fits close. I wouldn't recommend the really fuzzy fleece, however, because it tends to bind up on the fleece lining of the Gamma MX. I find the Atom LT to be the ideal layer, and that way you'll still have a bit of protection if you take the Gamma MX off.
Drawcord, yes.
Fleece, it's about equivalent to a 50 wt fleece.

Hi Levi
I'd say the Gamma MX has a slightly looser fit than the Epsilon,but is still trim. It does have way more stretch and is a bit warmer and more protective while still breathing well. I can fit a baselayer and a light insulator ( I use the Atom LT for cold weather) under my MX and I wear my normal size.

As Paul said the jacket is more air permeable but if used for what it's meant for, high output activities, it doesn't make much of a difference. I had mine out skinning in probably 25mph winds with 40mph gusts dropping the temp to around 0F and didn't feel anything. If you want breathability you don't want windstopper.

It does not have windstopper fabric. It uses fortius 2.0 which is a stretch woven fabric. Windstopper uses a membrane laminated to the fabric. Fortius breathes better than windstopper but is more air permeable. I am not sure if there are cfm numbers on the fortius fabric since it is a proprietary arcteryx fabric.

I don't agree. I am 5'7 155 lbs, chest 38-39", and the small is a perfect fit. It is cut so well it can easily fit a baselayer and 100-weight fleece underneath yet is also trim fitting with just a t-shirt. The Gamma is best with 1-2 baselayers then as a mid layer under a shell if things get extreme. I think a medium would be big -- recommend going with a small.

For a trim fit, the small will give you the best fit. I wear a medium at 5'11 170. I typically wear just a baselayer or a very thin insulator (Atom LT) at most. If you want to layer under this, espcially if you use fleece, the medium would accoomodate this better.

Thanks, I'll get a M!!

A small will not work, I've got a buddy is about your size and wears a medium.

Okay awesome. Thanks for the help! Also just curious... I have been looking at the Marmot ROM a lot for the same uses. It is a lot less expensive but how would you feel the two stack up against each other?

Both are about the same warmth (200 wt fleece eq.). The Venta is more windproof and does not breathe as well (but has pit zips), where as the Gamma Breathes better and has some stretch to the material (and more athletic cut) for active movements. Both will be shed some light precipitation, but will eventually get wet. You would probably find the Gamma More useful for your needs and have a few bucks leftover to pick up a nice baselayer.

It is an athletic fit, with a bit of stretch to the fabric. I can wear either size (with a 40" chest)- with a medium I will use it under a t shirt, with a large I can put a fleece or another layer under it.
If you plan to layer underneath go for a large- The waist cinches up nicely without looking ridiculously baggy.

I would not say it is darker than the pic- but this will also depend on your monitor settings. The color was just nicer in person than what the pic showed (maybe a shade or so lighter overall).

so roxo is a more darker purp than the pic?

Roxo is a deep purple. I find the color looks better in person than the pictures show.

Arc'Teryx experts on their site actually answered this. They said the new Fortius Fabric is much more resistant to fade as well as has improved breathing properties. They also confirmed because it was designed to increase breathing, it is not as wind resistant and possibly not as warm as the prior model. The Fortius 3.0 fabric in the Gamma AR is simply thicker and as such, is closer to the the prior Gamma MX

Dean, are your weight and materials specs for Fortius 1, 2 or 3?

Hey there, no not really, unless you are partial to Polartec brand... here's the scoop on the all new Arc'teryx created Fortius material:

Why the new fabric? It's made in a small Japanese mill and means Arc'teryx Jackets has more control over its specifications than they would dealing with a larger brand like Polartec. Ultimately that means better performance, they say.

It comes in three versions. Fortius 1.0 is a stretch woven fabric for high energy stuff, then there's Fortius 2.0, used in the classic Gamma MX and AR lines, which has a polyester brushed liner laminated to a stretch woven nylon face fabric.
The adhesive used in the lamination process adds wind protection but is still air permeable and very breathable. Finally, theres's Fortius 3.0 with a warmer liner used for the Gamma SV and aimed at real cold condition use.

Here's a breakdown of the specifics of the two materials:

Fortius Fabric is a stretch woven plain weave fabric made of continuous textured nylon (84%) and spandex (15%) filaments. It is extremely lightweight, weighing only 160 grams/m2 (4.7 ounces/yd2), breathable and quick drying.

Polartec® Power Shield®: A tightly woven nylon exterior face laminated to an inner insulation layer. Between is a breathable, discontinuous membrane that transports moisture away from the body. It is treated with a DWR (durable water repellent) to shed rain and snow.

Since its directly designed by Arc'teryx personally it makes the new material sound very promising...