I don't have any experience with the G&L, but every ultimate I've seen flies great if you get enough power and keep the weight reasonable. My AW weighs in at 41lbs, with a DA150, Hyde soft mount, cannisters, carbon gear and spinner. Without all the frills, I think 39lbs, or a little less, would be reasonable. It originally had a 3W-200, but it weighed 43lbs with that, and the performance was the same overall.
If you do the unloaded TOC style snaps, the unlimited pattern is not a problem with a 150. It's still more of a challenge than a lightweight extra. If you do a traditional fully loaded snap on the up-lines, it bleeds half its speed aft one, and is down to a crawl after two snaps. It looks just like the real plane. Unfortunately, it's a work-out on the sticks, and the IMAC judges don't give much credit for the realism. Learning the unloaded snap technique is a must in unlimited. In the other classes you have ample power regardless of your technique.
I am at 600ft here in TX, and have never flown at 5,000ft pressure altitude. I would guess you would have to be very light on the sticks with the loss of power and lift. Another option is the 3W212. Your plane will take a 4lb hit, but your wallet will be about $800 lighter!?! There are several 100cc size ultimates coming out (AW being one) that look like they have a better thrust to weight (and cost) ratio.
I checked my throw for snaps, and they look like this: Elevator is 8 degress, rudder 12 degrees, and ailerons 35 degrees. I got these by reducing the throws each flight until the plane wouldn't snap any more, I then increased the throws back past that point. CG makes a difference. The more forward it is, the higher the throws have to be. The boys at AW say they prefer a forward CG. Mine is too far aft, but I would have to add weight to bring it forward.....so I'm living with it aft.
Glad to hear there are other bipe guys out there!

CJ