Did you enable the hardware mouse option they added?
I hear most people run at 2xMSAA. 4+ seems to really start lagging.
(The Devs said they have an entirely separate team atm dedicated to tweaking; even recoding the engine/game while they work on ps3 version; hopefully that helps many)
Drivers, System checks ..etc..you probably did that all already.
I hear there are port options now for the client with the config; never needed to mess with before so don't know if that helps.