Even you use the rip or the iso, you can update to v436. The update installer asks for the game path and don't look for any correct previous install of UT.
v436 NoCD are fully available on the WEB.
I've a GeF5900 and pb is the same.
But it's always possible to get normal framerate when restarting the game; I've finished it few weeks ago. Seems to be an engine pb...