What thickness of acrylic? I think just under 1/2" would be reasonable for an 8' tank with 1/2" acrylic. I had a 370 with 3/4" acrylic and I bet the center bowed just under 1/2"...
EDIT: Nevermind, the guy who built my tank posted in your thread, so I'll shut up:lol: You are in good hands with James!