I have a TDC 6x6 projector, which came with an 35mm insert as well, and a home made 6x7 projector. It really does make a difference when you project them.
Had fun with the 6x7. Went to show some slides at my friends house, started in the basement which let us get about a 7 foot square picture. Friend said they're great but how large could they get without looking bad, so we went to the back yard and put them on the back wall of the house which gave us about a twelve by twelve frame,and they still looked good.
Then we went for broke and went to the garage side of the house and put them up there. Had to be 20 feet across and you could still see window frames ,blinds and even the writing on the back wall of a church altar.
It was like you could step into the picture