If I remember correctly, 645 will make 8x10's with no cropping. What do the 645 enthusiast's suggest.
Remember that the formats are all nominal, and vary from maker to maker. For example, I love Linhof's 56x72mm format which at a 3x enlargement is 168x216mm i.e. almost exactly whole plate. Other '6x7' formats go as low as 56x68mm in my experience, and lower for all I know. '645' is typically 56x41-43mm, but can be more or less.
I use 6x4.5 as my primary format, although I have been moving toward more and more 4x5, and 8x10 recently, and I have to agree completely with Matt. Don't make the choice based on something like that - choose the system that does what you need for the price that you can afford.