In that case I may as well just crop - since that's effectively what's happening anyway.

Hmmm - i'm actually curious what effective megapixel the 5d's 13MP image cropped down to aps-c size gives me.

I do need to consider a backup body soon - i've got a d30 at the moment - but when i'm out shooting with the 5d in situations where i'd need/want a backup body the punt from 13mp back down to 3 is a bit harsh (plus, the folks that I do some of my shooting for don't want anything less than 6-8).