I'm running two of the Swiftech MCW82 s on my machine. I'm generally happy the performance of them. The only wonky thing about them is there isn't good clear documentation on which is the inlet and which is the outlet. The machining on them is also typically not the cleanest. It's a pin array and on my two blocks there is variance between rows of pins. It's not a dealbreaker, I don't see it unless I pull the block apart and it still works acceptably well with my 6870's clocked up to about 990MHz; they stay cool at sub 50 degrees C under load. Sidewinder has the MCW82 for $48(US) currently.
As for flow rate, I can't tell you anything definitive. I've got a pretty big loop (2 3x120 rads, 2 gpu blocks, Cpu block, big reservoir, flow sensor, two pumps, and a LOT of hose). Check my project thread if you want to see the scary thing I made.

I would avoid EK on principal frankly. Although you are wise to go copper only if you choose to go with them. I HAD a nickel plated EK block in my system. That changed when I discovered it was corroding.
It also appears that Sidewinder sells an XSPC Raystorm universal GPU block for $60. That may be another good option. I haven't seen anything either way about the block, so I have no opinion on it. Might be worth a shot.
Hex.
[ "I may not have a 'med school degree', but when you get shot, you'll be happy I'm here..." -- Dr. Zed ]