Nice results.
Water cooling had the same effect on my 6850s but not to that extent.
With stock cooling I could only overclock to 960mhz for 245Mh/s each card. And pulling 448W from the wall.
After water cooling use 2X Antec 620 coolers I got for $80NZD each.
Could overclock to 1010mhz for a 260Mh/s pulling 440W from the wall,
Cards with stock cooling were running up to 78C, After using the 620 water coolers they were running at 45C.
Got some air ducting so the radiators draw in air from out side. Bought the temp down to under 40C and also allowed me to overclock a little bit more to 1030mhz for 272Mh/s each card at 450W at the wall.

So I went from
490Mh/s @ 448W
To
544Mh/s @ 450W
for $180NZD with 2X Antec 620 water coolers. Also PC is whisper quite.