I just did exactly the same (and I guess you will buy from the same company and have the same guy do the ISF calibration). My subjective opinion is that going from my old to the new projector was really great, and images are really natural and saturated. You would need to ensure 16-235 levels for the entire signal chain (no 0-255 anywhere) to get the grey scale right.
Also, when having a ISF calibration you get most of the way there (90-95%?). The rest must be adjusted for at your house to take into account wall reflections, projection screen performance and such. I would assume that inhouse "errors" would be larger than any colour discrepancy introduced in software. But that is only my assumption, and I would love MC team to enlighten us on the subject.