you won't see a difference in the performance of these blocks, most likely you'll looking for quality of the block and EK has a better quality built compared to DD, I'd put my money on EK to worth a while!
There's a thread either here or over at XtremeSystems from a guy that opened his DD8800 after a few weeks and found a bunch of crap that was building up on the rough edges of the poor machining on the copper channels.
When you see the EK and the DD opened up, side by side, you'll know why everyone says get the EK. The copper channels are much deeper, the machining is beautifully crafted and the overall build quality is much much better.
The prices are comparable but the quality is not.