I say this with all due respect Tim - a turbo upgrade ain't free either....numbers help decision making....I know I would buy one if the power gain was significant (I could care less about economy)....
Gotta pay to play, beside I ain't selling em, amusing how many other things bought on blind faith ie SSD's 80hp that ain't making that, cold air intakes that suck in hot air supposedly making huge gains etc.; since you are a regular at the track maybe your data would be worthwhile, you could get one and try it if you didn't like it I'll surmise you could get your money back out of it.
I've bought 2 now on faith Mitsu & ATT, not really faith just doing the study it made sense to me that they would be better, and cost was less than any other option out there, I've got $1500 on a custom IC setup that no longer serves a purpose because prevailing wisdom at that time was it was required at maximize the GM-8 performance, different technologies now prove that wasn't necessarily so, at time it was a good buy for me, IMO the ATT is smarter money spent, I wish it had been around back then, but remember this turbo was never talked about as a race turbo, so I doubt of any interest to you, but hands down a far superior turbo for towing and mpg,
As far as power goes I can only attest that with GM-8, my pull 2000# 6x12 enclosed trailer last weekend to my hunting camp was a whole different driving experience, with ATT I lock cruise control and forget it boost smoothly adds power, vs hard spool up & down & downshifts to to make top of a hill, how much extra power I can only guess, possibly exact power, but it is derived better/more efficiently with ATT, with ATT dropping CR is not necessary, so one saves by not needing to lower CR, no aftercooling is necessary, and less stress overall on engine as boost does not have to be driven as hard to get the turbo to make up for lost efficency, and with improved mpg it can pay for itself.
