At a guess I would say not a hell of a lot better than decent air cooling. The 3750 does tend to run a bit hot when it's over clocked so would benefit from being watercooled. On the other hand the i5 runs a lot cooler so would benefit less, but in a loop with the 670 it would be worth the effort and it will look good as well.
thinking just doing the cpu as its much less effort then dismantling a gpu. also no waterblocks for gtx 670 asus dcu2 both ivy setups just to include the gpu or not
thinking of using this http://www.specialtech.co.uk/spshop/customer/product.php?productid=15990 with fractal arc mini case. its only got 2 front bays but i don't need them. bit lost over radiator size was thinking going for alphacool 240 as they do 2 sizes 45mm and 30mm thick and have several connection methods. 4 inputs/output http://www.specialtech.co.uk/spshop/customer/product.php?productid=15353&cat=2036&page=
http://www.youtube.com/watch?v=PUByJCd-y7M&feature=channel&list=UL can fit a rx240 in the roof as im using low profile ram
