The £279 card I linked to is absolutely ideal tbh. 680 PCB and the vapor chamber cooler. You certainly won't be hindered with your overclocks as it negates using the 670 'add on' cooler with the plastic extension.
Also you get the benefit of having the PCIE power connectors at the end.
If it had a stock 670 cooler and PCB I wouldn't suggest it but the vapor block in the 680 cooler is much bigger and can tame a 680.