20 sounds like a good gain, if that's possible. The largest gain I have seen on a N/a E90 is around 15. Everyone else has said that anymore is reaching.
Keep us updated if you get anymore news.
M-tech E90 330i JB/TERRA modded - RIP
n54 135i AW/CR JB3 FBO 420whp 444wtq - 11.5 sec 1/4 mile @ 122mph - RIP
e53 X5 4.8is M///BLUE/M///SUEDE - 357whp 369wtq - The Snow Beast!
n54 135i JB/CR JB4 FBO - Tc Kline D/A Coils - 1/4 mile/dyno PENDING