I ride a 53t biopace with an 18t EAI cog for 77 gear inches.
I love it.
I adjust my chain tension for about 1/8" play at the tightest point, which gives me about 5/8" play at the loosest point.
Biopace has spoiled me.
I should probably buy another one as a backup for when I've worn out the one I have.