Is there a reason why you are changing to liquid cooling? Are your temps getting too high even with those VaporX coolers on the 5870s? If you are not having temp problems, why spend more money and take the risk of destroying everything with a leaky tube?
Other than hooking up a large radiator with a large, quiet low RPM fan, I am not aware of any substantial benefit to liquid cooling anymore.
I agree, you can get really good results from a high grade HSF. Unless you're just wanting to run liquid. I would like to, but just can justify the expense, risk and what little I'd gain. Sorry if that's a downer.