I'm sort of in the same boat...I'm still living with a P4 Northwood myself...but I've already bought the i5-760, motherboard and RAM...(delivered last week) I MAY just return it all and wait for the SB release, but I suspect the i5-2500K will be quite a bit more $$$.
http://www.semiaccurate.com/2010/11/22/sandy-bridge-pricing-leaks-sweden/
"This brings us to the first K model, the 3.3GHz Core i5 2500K which is priced only slightly higher than its non K sibling at SEK 2328 or $337 with VAT or about $270 without."
The i5-760 was just on sale at Newegg for $180...and motherboards are available for the 1156 at reasonable prices.
AFAIK, there's no reliable info on motherboard prices yet either, but if they're priced like the 1366 boards...then $200 will be the beginning price for GOOD boards...