i have no problems with adding a gpu to the loop (i already have the loop so all i need is a new block any way)
But i wouldnt bother doing it unless i could and was messing with the bios to adjust TDP..
The TDP of a card will always throttle the stupid thing even if its at a perfectly adequate temp because of the other variables "voltages etc" once it starts using a bit of voltage which would generally be enough to produce more heat than the stock cooler could dissipate the bios throttles the card.. after all it does not know that you changed the heat sink for a water block.
Without changing the TDP on my 780 my max oc clocks without throttling was the same if i had air cooling or water cooling, the only difference was temps. After changing the TDP my self (all other bioses you can download locked the voltages so you had no idle mode i did not want that) then at the same voltages i could push the card much further (within temp restraint) i didnt even need to adjust voltages.
But without risking potentially bricking my card to change the tdp, there was absolutely No reason to water cool it.