MOHAA: type "fps 1" at the console.
RtCW: type "cg_drawfps 1" at console. (Not exactly sure about this. Not at home to check CFGs.)
It's amazing how chuggy MOHAA can get at times. In an outdoor level with loads of fog and trees, I'm getting ~15-18 fps with a GF3ti200 and an AXP 1900+. Yipes! Of course, running at 1024x768x32 with EVERY option cranked to the MAX and Quincunx FSAA and 16-tap aniso turned on can't be helping. Otherwise, it's been quite smooth, but it's gotta be a slideshow for less p1mp3d rigs!