I dunno, my experience with stock turbo vs ls1 T/A's ahve been me losing quite a bit. When I had a very aggressively tuned map with the stock turbo from a stop i could hold em off to about 90-95ish and then they'd walk past me pretty good. From a roll they would pull off the jump and not let me pull on them at all. It took me alot of HP and aggressive tuning with a vf34 to pull only 2-3 cars on this T/A from a roll. This is on 110 octane gas, 22psi, VERY aggressive timing and fuel(I did have 3 people inside my car however with all windows down). Properly driven, a very basiclaly bone stock LS1 can usually even hang with a 30/34 stage IV wrx. My buddy weedy and I a long time ago in his car(vf30) ran a SS camaro from a dig and only pulled about a car on him. LS1's are no joke top end mofo's. I hate running them because as stated earlier, you hav eno idea what you're racing. They could just loud exhaust stockers or heavy modified sleepers that run 11's. But hey, that's all the sport right?
And about the T/A being heavy, keep in mind our scoobys weigh what? 3200 lbs i believe? That's pretty damn heavy for an AWD car from a roll to be taking a LS1. Plus the fact that the design of the WRX is like an aerodynamic breadbox compared to most other sportscars which makes us from high speeds have a lack of top end unless you got one big giant snail under the hood!