Thanks for the replies. I was basically checking the question on whether they're in the same ballpark enough to go ahead and just use the 5600+/4870 for the higher end system (I have this big case for that one), or whether it's unbalanced enough to use them for the lower system (Sonata III case), and to keep shopping for the higher end CPU over coming weeks or months, and plan to move the 4870 to the high system and get a better match for the 5600+ (cheaper too) when I do that.
I've got a confused approach anyway, along the lines of 'bought more cases than I need because of good deals, and sort of want a computer room gaming PC and a PC for the living room 65" LCD used for big screen gaminig and home theatre use, but I haven't really figured out the logistics especially what surface to use for the keyboard/mouse, and in the meantime these cases sitting around are getting annoying and wow is too slow on the ancient PC'. I snagged a 4870 1GB for $219 and a 5600+/ECS MB for $66 over the last bargain weekend and there we are.