I'm using a dual dual core 3.4Ghz Xeon box and B6 pegs both cpu's and all 4 cores at 100%. In comparison, I was using a dual single core 2.4Ghz Xeon box for B5(yes B5 didn't use both cpu's),..........I have a B5 file that the 1st pass rendertime was 7hours and 12 minutes on the older machine,..........on the new dual dual core machine, same file loaded into B6, 1st pass was around 12 minutes. B6 has  very good multi-threading utilitization ! So I wouldn't wait,.........I don't think quad cores are going to be out for at least 6 months or so,........maybe longer and as it's newer tech, it'll cost considerably more. Just my 2 cents worth.

"Any club that would have me as a member is probably not worth joining" -Groucho Marx