I'm a bit confused.

I have a  GTX 560 Ti

With  -l f25x23, I get 294501 khash/s, but the GPU is hardly in use.
With -l  F1536x16 I get some out of memory errors at the start, but it works, giving me 75284 khash/s. The GPU is using about 80%

Is the f25x23 doing it's job?

Thanks