Go for it!
I have found the Core Layers from Sitka to be the best undergarment, period. I have tried from Under Armor to wool and there were a LOT of choices in between.
I wear my core layers when training for hunts all summer long. They keep you cool when it is hot!
The Ascent Series is the one I would choose for an outer garment for GA. It will keep wicking the moisture off you. As an added benefit, when it gets cooler and you want an extra layer, the 4 way stretch will still allow you flexibility.
I'm on the field test staff for Sitka and have been wearing and testing it since early in 2007. They keep improving it and I have not been uncomfortable on a hunt since I started wearing it.
I know A&H Archery is now a dealer for the gear and is offering free shipping. They are a fine sponsor of TradGang!