It has made a difference in mine and I know CRE has said in his. I haven't been able to dyno mine again to see how much difference. The throttle responce is great.
The thing about the Maft-Pro with a wideband is you can tune it yourself. With a GE it is a longer process to tune than with a GTE. I know I couldn't have tuned mine, which I'm still working on, without CRE's help, but I am a little challenged technically.
It makes a good addition to a GE if you have moded a motor, i.e. cams, ported head, bored, stroked, the Maft-Pro is what I would suggest because you have changed enough that a stock ECU is just not going to cut it. Mine would run, just not very well.
I could guess around 20 more at the wheels +/- a couple.