AT WOT the O2 sensors are not used. The fuel mixture is based upon two things one is MAF count and the other is LTFT. If the O2 wasn't getting a good reading the car will throw a code quickly. You will get a code of Lean bank #1 or #2 depending on the affected area. Your best bet is to tune it on the dyno but if you had a logger you could see how much correction is taking place by the ECU. You may see the LTFT's are -10% or even possibly +10% trying to compensate for a tuning problem.