My 2 mountain bikes are setup with 7 speeds spaced as 8 with 8 speed shifters. Been running this setup and it works perfectly. The derailleur does not shift into the spokes. Setup is easy, setup in first and rear limit screw is properly set so it stops at 7.

I have not tried 8 speed shifters with 7 speed spacing. Can't imagine I'd be happy with the poor indexing. I'll tweak 1/4 turn on barrel adjuster to dial in shifting so hard to accept built in inaccuracy. Maybe others can accept less than ideal.

John