Take a look at BladeRunner's site and see by yourself, with good wires it wont cause any problem. Those switched PSUs are *not* tightly regulated. It's the exact opposite -> mosefts are that hot because they're given totally out of range voltages (due to the switching loop just before them).
So if you *need* to extend them it's ok. - just make sure your solders are good (theyre usually the weak spots) or they'll melt / oxyde under heavy load on the 12v.
And keep us informed
Post photos of your watercooled PSU !!