the 780 classified can easily pass up a reference 780ti and most out the box 780tis. but if your going to water cool you would be better off getting a 780ti classified kingpin. there is really no point in watercooling any other 780s except the lightning... the rest are either voltage locked or dont have the power delivery design to provide stable overclocks.
otherwise, i have benched it at 1375mhz@1.25v(133% power target) for quick unigine/3dmark runs, my 780 classified has a limit at about 81c in gaming a 1.212v@1300mhz core all on stock air, skynet bios, but i keep it at 1.20v@1250mhz and stay under 75c.
i dont really see how the higher ones are out of your price range. it will cost $350 for a d5 pump 240mm rad and an ek block for whatever card you choose... that still makes the regular classy about $900 just to get very high but stable clocks. another $125 for the ti version just makes sense at that price, or preferably the kingpin.
either get a regular classy and get as much out of it on air as you can or go with the kingpin and hit 1.6ghz under water, at which point it is very close to the performance of sli reference 780s.