Good points all. I loved my past projector but as you mention I didn't love the need to keep the room fairly dark to get the most out of it. This new set up will get a fair amount of regular tv viewing which also makes me lean towards the 75" set up.I tend to prefer non-projector options, myself. As Flint says, the picture quality tends to be a little better at the same price points. Also, projectors tend to require darkened rooms- IMO, I don't necessarily want to commit myself to always having the room dark and be focused solely on what's on the screen.
For me, the one big (biggest) issue about putting a large flat panel in a home theatre is having to therefore compromise on the audio layout.
A projector and acoustically-transparent screen combo, while more expensive, eliminates that compromise, for any given speaker system.