Have you had it properly dynoed...
I noticed a big jump in the mid range as Tim from RPM said that it was running real rich when on full boost so he fitted the Bleed kit for the Fuel Pressure Reg. and well I gained 10rwkw.. up top and a good chunk in the mid..
That flat spot may be it either pinging or over fueling, if you can't hear it pinging its probably over fueling.. and I guess if it is over fueling the bleed kit will set the af ratios correct..
for $70 fitted its a good investment..
With slight mods you have it probably isn't worth getting the SAFC also I'm not sure if the APEXI SAFC supports different oam injectors.. Get a Fuel controller that can run different injectors..
I'm still learning so some of the gear I've said Could be wrong but... its what i've concluded.
Eathan was it you that said you had wheel spin problems a while back? If so did you try the retreads.. ?