So got my Used OEM heatsink and turns out the screws with the MSI Gaming ed Gtx 780 are not compatible with the OEM heatsink. Fortunately I have the screws from my 7970 that under water. So they more or less worked nicely.
Second I noticed the PCB had a slight scratch exposing the copper. It didn't look deep so was hoping it was just superficial. Guessing a dab of clear nail polish should seal it. Also the PCB on one end looked like there was some liquid that had dried off. At this point I am just crossing my fingers and hope the card works.
So anyways I fire it up and no video. And I am look poop I got a dud. However I reset the bios and viola I have video. However at this point it doesn't really mean anything since the drivers weren't loaded yet.
Patiently install the drivers reboot machine and so far so good. But only a nice run of 3Dmark 13 will tell me if the card is working correctly or not.
So did a few runs of 3DMark 13 and scores around the 8.7K mark. Which sounds normal.
Next I noticed my boost clock goes all the way to 1045Mhz but throttles down at 80C. At first I thought my Heatsink install was not making proper contact but turns out this is normal. Also my fan wasn't ramping up as much as I thought it would. Probably the fan profile was tuned to the MSI Heatsink fans.
So I changed the fan profile in MSI burner and viola. Card now stays around 70C on load with boost staying at 1045Mhz.
Overall a very happy camper
http://www.3dmark.com/fs/883929
BTW the factory heatsink is one of the best I have ever seen. The fan even on 100% makes a nice whoosh sound compared to the jet engine on the 7970's