I also would keep the PSA upper, especially if it has the CHF FN barrel, but even if it doesn't. I have a PSA upper with the FN button-rifled barrel and love it. It compares very well with my BCM upper (button-rifled barrel) and Daniel Defense upper (CHF). (All of these are midlength, not M4 profile and carbine length gas.)
I have no comment on the DTI, it may be very good but I know the PSA is good.