8x6 would be ideal for me.
I would then feel, um, powerful.
I do now mind you, having done enough PE to discover what works for me, and that I just keep going.
My wife has experienced both and has never mentioned the difference, though occasionally she will push me back slightly as I might be making her uncomfortable somehow.
Began December 2009 at 5 7/8" length and 5" girth.
As of December 5th 2012 7 3/8" BPEL and 6 1/8" base girth.
Going for the magic 8"x6"