Hello NWSRG,
Lemurian answered the question for me. I am not a technician, but yes you do get engine intermixes. That is, let's say two "different" CFM 56's. They both would have the same thrust, but they might have different FF, EGT, and possibly a slightly different negligible GND IDLE. But other than that there's not much diffs. The other difference is the restart envelope, the SAC being the better performer.
The SAC is more environmentally friendly and thus where possible, the older DAC's are being swapped/replaced/modified slowly but surely.
I think that on MD 80/90's it is/was common practice to have different engines on one A/C. I thought that I once saw an SAS MD80 or 90 with a V2500 and an older smaller engine (P&W?). I might have seen incorrectly.