suggest your over and under load problems are due to the KFDIMX map not being correct. Altough the compressor is still a stock size the billet wheels are hugely more effecient and can easily power upto 280bhp ( larger turbine needed though) because of this the ECU struggles.
KFDMIX is driven by target boost , which is correct and stable at all rev range, just load is not matching. So as i dont know how "calibrate" boost calculation to suit true load of modified engine , i did oposite = "manipulate" load to suit boost of factory engine. Its worse way, but i want to prevent some load error issues.
I dont have personal experience with billet wheels as much, but if wheel is physicaly-design identical to factory, only have little less weight and have extendet tip, i dont expect any massive gains. All benefits are only "teoretical" to build more hype people to buy and put inside their factory turbo. My opinion. Never personaly(not internet) seen or tune 280bhp in real even on K04-23.