You are wise to go with 42s, recal your Bullit meter, get the chip burned for your new meter cal, & run the 255 in-tank pump. It's a big nut to crack but worth it IMO.

For those who don't have an injector upgrade in their budget, there is also an old-school method of tuning with your FMU besides the recal: install an air bleed valve on the line going to the FMU. Vortech sells their own whoopy-dee bleeder valve, part 6Z120-010. I doubt you were getting much more fuel in the motor at 90psi than you were down at 65-75 psi, in fact a pintle injector can actually lock wide open over 80 psi if you don't have good electrical grounds and high enough throwback current at the injector, something to watch out for. You can roughly gauge how much fuel you need by calculating what your present injectors were delivering at your torque peak, which is the point maximum fuel demand.