As seen here, when it comes to super-fast memory clock speed and/or aggressive memory timing, neither makes a huge difference.
If I read this article right, the best way to make a very fast machine is to invest in (in order of "bang for the buck"):
(1) leading-edge video card (FOR GAMERS, irrelevant for Vegas);
(2) fast hard drive (i.e. WD Raptor 10k rpm, $150);
(2) fast processor (AMD x2 whaterver, $300-$800);
(4) fast memory.
If I read this article right, the best way to make a very fast machine is to invest in (in order of "bang for the buck"):
(1) leading-edge video card (FOR GAMERS, irrelevant for Vegas);
(2) fast hard drive (i.e. WD Raptor 10k rpm, $150);
(2) fast processor (AMD x2 whaterver, $300-$800);
(4) fast memory.