Only registered so I could say thanks to the cudaminer guys but can't post on their thread so I'll do it here, and hopefully help some other newbies too.
I just updated to the 12-18-2013 version of cudaminer and my 2 x GTX670 FTW card rig and I'm seeing an massively increased hashrate from ~420KH/s up to ~630KH/s!
My settings are +40Mhz GPU overclock, -500Mhz memory underclock, everything else default. Cudaminer settings that work for my cards are:
-H 1 -i 0 -m 1 -l K14x16
Temps are up from the old version where I'd run at 69C all day long to 76-79C, I get possibly very slightly better speed with K7x16 but it makes the cards run 1-2C hotter which can tip them over into the next GPU clock throttle point so it's more variable.
Maybe still not up there with the AMD GPUs (especially considering the purchase price of the cards) but I bought this machine almost a year and a half ago for gaming not mining and given the GTX670 only draws 180W per card, which by my calculations is about 1.72KHash/W not far off the 7950, I'm pretty happy with that.
NOTE: You need CUDA 5.5 which means you need pretty recent NVIDIA drivers, update them if you're not seeing a performance increase from the previous version.
Download:
https://mega.co.nz/#!BUwCCSDL!JArHK18d7h3JYxNIolKj_xzYcpBrTgff20LYE7JE4l0
CUDAminer Thread:
https://bitcointalk.org/index.php?topic=167229.msg4020077#msg4020077A Reddit with lots of peoples settings:
http://www.reddit.com/r/litecoinmining/comments/1t65as/nvidia_kepler_mining_improvements_now_in/Thanks to Christian and Dave for their awesome work!
Donate to them here:
BTC to Dave: 17sb5mcCnnt4xH3eEkVi6kHvhzQRjPRBtS
LTC to Christian: LKS1WDKGED647msBQfLBHV3Ls8sveGncnm
Have a nice day guys.