You need an ECU from another 325'e'.
the ECU number will end in "027". To upgrade it to +24hp/28lb. Ft., you will need a Turner Motorsport chip. If you decide to go with another manufacturer...Racing Dynamics also makes a chip, and a few other companies out there. Just the JC is the most reputable, and most common...so you will find lots of people with experience with it.
As for a "performance ECU", I don't believe one exists...unless you go to a several thousand dollar after market engine management system.
The only company that makes an ECU chip for your car (your ECU number should be 0.261.200.021 and be 24- or 28-pin) to my knowledge is Racing Dynamics. I have this part also, but it will net you only 17hp...and it is more expensive than the JC chip by about $50. It retails for $249.95.