Re: Arena mode kinda stuttery
Well, I have the same problem with SiN in general as well, and I'm on an X800 XT.
The Dock areas (lighthouse area, etc) drop significantly, as do all the Arena maps when the combat gets going. Little things like when the semi truck turns its headlines on before trying to run you over kills drop the framerate to roughly 20ish as well. I too have tried lowering all the graphics settings to no avail.
I'm hoping it's because SiN is using an older version of the Source engine, and all these problems will go away after the upgrade to the new version. I hope.