Hey there OP I run a GTS 450 and get 70Kh/s on stock settings. It's a coincidence that I just overclocked my card for the first time and you're here
I increased core clock ~17%. From 810Mhz to 950 Mhz, which jacked up my Kh/s to 80. Also tried on 970Mhz which got me about 970Kh/s but I love my card so sticking to 950Mhz.
What brand is your card btw?
Is there a way to check, on MSI afterburner it shows MSI GTX 660 Series.
I'm not sure if thats it...
Edit : NVIDIA Geforce GTX 660