Will a upgraded ecu such as a M2 stage 3 actually maximize hp besides adding fuel. Would adding the ecu make notciable power changes?

 

No. The only way the chipped ecus allow you to make more power is that you can run higher boost than stock.

EDIT: Actually, you MAY make a few more hp (not significant) at 10 psi, as the chipped ecus probably run a hair LEANER than the stock ecu at 10 psi. They may also have more advanced timing than the stock ecu, which uses VERY conservative timing in the high rpm range.