I'm running GT 650M in SLI (mobile graphics so not as powerful as 650 GTX, but SLI gives it a chance) and I've noticed that frame rates are significantly lower in the latest alpha than previous ones. For reference, then only went < 40 fps in the big single-player battle in alpha 1.0, but they seem to now be consistently lower than this in the MP scenarios. Not to the extent that Steve is seeing though.
The station kills my frame rate, though that's to be expected. We've heard elsewhere that there is a plan in place for optimisation of that. I've only managed to dock once, and it's the exterior view where things *really* slow down. I haven't measured (difficult when you can only get to the station 1% of the time) but would estimate something in the region of 10 fps.