If they are getting any gains its next to not noticable. I got tuned with a DP and stock CBE, good numbers, then switched to a cheap CBE, which hurt me as it had a leak, then got the Cobb CBE with the Cobb DP and never got another run, but didnt feel any difference which means if there were gains it would have been hard to quantify on a dyno as the time, temp, all that was different so the numbers would have been different.
Get a good TBE, IC, 3 port BCS, injectors, and a good tune and you will love the car.
"2007 WRX- PPG'd, 20G- Tim Bailey tuned
Stage 2 2005 WRX