Neh.. Dual P3 1 Ghz = Uni P3 1 Ghz in almost any circumstances, unless the program is being written multithreaded. The only program is so well multithreaded is RC5 Client as far as I know. Q3A written multithreaded, but can't show it real potential in any Video card as far as I know.
It is like saying, you need 10 min to convert a WAV to MP3, it will still take 10 min to convert a WAV to MP3 on dual processor combo. Except, when you convert two WAV to MP3, it will also take 10 min on dual processor combo 😉
Speed up? Neh.. very rare.. unless specifically written in multithreaded.
Do more stuff in the same amount of time? Yes.