No there's no fps cap when running timedemos.
AFAIK there's not been a version of Q3 where timedemo didn't work though some versions ago, "demo001" and "demo002" were replaced with the demo "four" (which is pretty much as system taxing as 001 and 002).
The latest version 1.31 doesn't include a demo but you can get 3 demos (in a single .pk3 file that goes in the baseq3 folder) from
here (the UC Benchmark Demo Pack 1.31). The 3 demos are "four" (converted to 1.31) and 2 others that are considerably harder on framerates than demos 001, 002 and four.
Just ran them on my 1.2GHz, GF2 GTS, WinXP and got:
four - 99fps
ucguidedemo1 - 63fps
ucguidedemo2 - 42fps
Also, I've never heard of entering "disconnect" before running a timedemo, I just:
\timdemo 1
\demo demoname