I went 6.1. It was mainly bad advice from a salesguy, and I was particularly green at the time, so I didn't question him. My rear centre is actually a centre speaker, the Athena C1 (sold singly). It sounds great to me, having it back there, and I DO think it adds something. Sure, I wish I HAD gone 7.1, but ain't nothing shabby about 6.1. I love mine.
cheers,
supervij