I contacted Big Agnes and asked them a similar question, about switching the included poles with carbon fiber poles. Here is Chris Tamucci's answer:

Thanks for the email Russ. The poles only account for some of the difference in weight. A lot of weight savings between the tents is in the fabrics and hardware used on the tent. I suspect that a Seedhouse SL3 will be lighter than a standard Seedhouse 3 with carbon poles. The carbon poles for a Seedhouse 3 cost over $200 and from what we’ve seen shave about 7-9oz. There is a 19oz difference between the two stock tents.

Just something for you to consider. You’ll get a lighter tent for less money by purchasing a stock Seedhouse SL3.

also the crossover pole is a shorter one that just keeps the fly off of the tent wall not the kind in the SL3 that goes all the way over the tent. There is also an additional pole that goes gives the vestibule more structure and room. It weighs a bit more though

Looks to me that the only difference is the pole material. Thus, you are paying $180 extra for one less pound in your pack.The poles are the major difference. The SL series use the DAC Featherlite NSL pole system & the standard Seedhouse series use the 7001 aluminum poles which increases the overall weight by 1.5 lbs. & yes the price difference is $180. If you want to lose the extra weight, you have to pay for it!

A 'seam seal' is a coating for fabrics that makes it waterproof at the seams. Most materials are relatively waterproof on their own, but having sealed seams is pretty important.There are a couple of options. One is to seal the seams yourself. Something like this item will do the trick.http://www.backcountry.com/store/MCN0004/McNett-Seam-Grip-1-oz-with-Brush-Applicator.htmlAlternately, I absolutely love my MSR Hubba Hubba HP tent. Most other people love theirs too. Take a look at the Hubba Hubba and the 3-person Mutha Hubba and consider getting those.http://www.backcountry.com/store/CAS0358/MSR-Hubba-Hubba-HP-Tent-2-Person-3-Season.htmlhttp://www.backcountry.com/store/CAS0421/MSR-Hubba-Hubba-Tent-2-Person-3-Season.htmlhttp://www.msrgear.com/tents/muthahubba.asp---- SOmeone else here - I disagree, some tents, though not seam sealed are still waterproof. This is basically arguing semantics though. Big agnes does not use the same term that MSR does. Check out Big agnes' site and see for yourself - http://www.bigagnes.com/str_tents.php?bid=8Also Bathtub floors are one piece, they are no seams so there are no need to be seam sealed.You will notice that if you pay 400 bones for any tent they are going to keep you dry. I love my Big agnes tent. MSr are cool but man this seedhouse series is insane and super light.Seam sealing new tents in 2008 is almost totally passe. Most of the high end tents have been factory seam sealed for quite a few years now.