I would try installing the drivers on a clean boot
and hitting advanced install and then clicking clean install. Only install the driver components you absolutely need
(linked to a good install guide for Nvidia drivers) like just the driver and physx. Please temporarily shut off your firewall and antivirus during install as well. It sounds like a long process but it really isn't bad.
So if you didn't do this I would try that. The clean boot should take care of this but always make sure you don't have precision or afterburner processes running during a Nvidia driver install. They can corrupt the installation. Just re-enable them after the installation. Also, as others said I would make sure temps are in check during gameplay.
I don't run SLI but I have heard you actually want the least performing/slowest card in your #1 slot when overclocking. But as you got a crash at only +4 I would suspect a bad driver install.
If you're on Windows 8 one thing I have found is that I have to clean boot and clean install all my drivers (like I described) and software to get it running right ex. my Nvidia drivers and my Logitech drivers etc...
EDIT: The 326.01 drivers
seem pretty stable and they do support the GTX 760's. They say for windows 8.1 but people have them working in 7 as well. I used them on vanilla 8. You might want to try those if The clean install with the other drivers doesn't work. Please clean boot and clean install those drivers as well if you test them.Edited by andydviking - 8/4/13 at 11:39pm