La Sportiva Nepal EVO GTX Mountaineering Boot - Women's - 2009 BCS

Regarding size - I wear a women's 6.5 to 7 shoe give-or-take and after Googling the crap out of "Nepal EVO women's sizing" and not getting a whole lot of guidance, ordered a 38.5. The fit was too tight for anything beyond a liner sock, so I'm sending them back for a 39.0.

I have also been in the sizing dilemma until finally I was able to try one on. I am generally a 5.5-6 or 37 and have a more narrow foot (hence found Scarpa did not fit me). I found a La Sportiva 39 suited me best (could do a 38.5 but they are so hard to find!) However, I am going for the 39 because I inserted my own orthopedic foot bed, I like to be able to move my toes to keep them warm and the size allows me to wear two thick (not overly thick) socks if I want. The heel gave me a good snug fit.
I got some good advice by the fitter. Your feet will swell not matter the temperature. Better to go a bit bigger than smaller as you can play around with socks and laces and the boots come with an extra pad that inserts over the top of your foot and ankle. It is important to have a really good heal fit that helps prevent forward foot movement no matter how much length you have or room you have for your toes.
Well that's my opinion.

Size up if you don't want very cold toes ... especially if you happen to have long ones.
I wear a US 8.5 or EU(DE) 39.5 usually. With my high arches (this boot is clearly not build for high arches, but you can leave this portion laced looser, and you can fix the laces above the arch and have the upper portion tighter), this translated to a 40.5 in these boots, which felt like the right length. However, when wearing middle thick merino socks over thin ski socks (the technical type, less thick than tennis socks) there was very little room in the toe box and the toes got very cold. With my narrow heel it is usually not a good idea to size up so I did not and spent a "refreshing" day ice climbing in 0F conditions, even with little wind. Can't imagine these doing well in extreme conditions unless you size up considerably with lots of extra insulation i.e. thick socks or maybe add an insole to reflect body heat. The cold seemed to be seeping in from the whole of the bottom/sole mainly, felt like standing on cold tiles. Don't think my high arches will be compatible with adding insoles but if you have flatter feet that may well work. Loved the narrow heel part. A less good fit for my feet but softer more padded and WAY warmer option was the Mad Rock "Alpinist" boot (men's size 8), no women's version as far as I know.

After painstaking research I chose this boot for climbing in Ecuador (over a double plastic). Happy to report that my shins and toes have felt great--worlds better than the beating my shins took in double plastics. People will give you mixed guidance on whether the boot is appropriate for that altitude (~19k ft)--my experience was good. My feet got a little chilly while standing and waiting up high, but warmed back up quickly.
I typically wear a 9.5 or 10 and ordered a 42 in this boot.

I have had this boot for two seasons now and have used them for ice climbing in the Northeast and mountain climbing in Peru. First, they are built on a womens last, so they are narrow in the heel and shug around the ankle, but have lots of room in the toe box. They are extremely warm so keep your feet warm when you are just standing around belaying. I have had no problems using them in lieu of a double boot for high altitude mountaineering. In extreme cold conditions, you could put a super gaitor over them. They are light enough so I used them as an approach boot to the glacier, so got a way without having to take two pair of boots. The lime green color is shockingly nice, too.