Prepare to see somebody with too much money OC 4 of them lol
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And cool them with liquid oxygen.
I only just recently bought four Geforce GTX 690's, if they wanted me to buy the Titan model they should have released it earlier. So the Titan can dance around my middle finger, because it's going to be 6 months minimum before I even consider putting down another £5000 for four graphic cards.
Actually your 4 690's is better, 690s are dual GPU cards and hence you have 8 essentially.
If you have them in a quad SLI I would be impressed if you have all 8 cores running at 16x. You only really need 2 SLI'd for all 4.