At part throttle, the new MAF or S-afc won't do anything because the ECU will relearn everything to get back to within stock specs. WOT is another matter.
The ECU ignores the O2's at WOT and bases the fuel and timing off of the MAF values vs. RPM on a preset table. Changing injectors, MAF's, and MAF values (via S-AFC, Calibrator, or the MAF itself) will have a profound effect because the ECU will not relearn these preset tables. If that is where your stuttering problem is, you could be in luck.
It's all good, what's it hurt to try, right?
Forgot to mention... at 212 to the wheels, you are very close to 100% duty cycle, at least by doing the math. Any OBD-II scans at WOT?
