Hey guys. I am new to water cooling, but I am wondering what are some of the best 780tis for overclocking under water to the wall! I heard that the reference one is generally used, but at the same time, I thought that it has worse power delivery than the non-reference options.
The Classified Kingpin has features available to serious overclockers not available on other "regular cards".
After that, it's down to the MSI and Asus.
Reference designs are popular with water block manufacturers as they can use the same WB for every manufacturer..... custom PCBs require custom blocks, but making them proved profitable at least in the top tier (...i.e. 770 / 780 in 7xx series)
Non-reference is starting to "go away" ..... non reference GFX cards came about as manufacturers wanted to provide more and better regulated voltages. The Asus DCII, Gigabyte Windforce and MSI Twin Frozr lines were good examples where they used custom OCBs with bigger / better VRMs w/ more phases to provide superior overclocking. The EVGA SC series stood out as the only major player to stick with the reference PCB. This started having less impact as nVidia put more and more restrictions (both physical and legal) on over volting.
Recently nVidia kinda "saw the light" and has recently started using an improved PCB design which MSI used on the 780 Ti to produce the best 780 ti available outside the Classified Kingpin.
I recommend the MSI for air cooled designs and either one for water cooled designs. Both are 10.5" long with EK Water Blocks. I'd use the Asus card w/ Asus MoBo and MSi w/ MSI if nothing else to make TS calls immune to the "blame the other guy" routine.
One more thing..... avoid the Hydropcopper..... it is quite poor at cooling the VRAM and VRM. There is a 30C difference on the VRM between the EK water block and the EVGA / Swiftech on the Hydrocopper....and 10C on the VRAM.
Water Block = Model EK-FC780 GTX Ti - Nickel 
EK-FC780 GTX Ti Backplate - Red 
EK-FC780 GTX Ti Backplate - Gold 
EK-FC780 GTX Ti Backplate - Blue 
EK-FC780 GTX Ti Backplate - Black