I wouldn't go for the DD block. Just did a review of it here:
http://www.overclocking.dk/litteratu...3549&type=test
I know it's in danish, but there is an UK summary at the end here:
http://www.overclocking.dk/litteratu...3550&type=test
Basically i was very dissapointed in the NV8 block, as is a lot of our users who have the block. It simply doesn't give you your moneys worth. I am currently waiting for an answer from DD as to how the temperature problems with the NV68 can be fixed.
Best regards