$350 for the 2600K wouldn't be too bad. Quad core thats unlocked and was seen pushing 4.9GHz on air sounds nice.
As for the Sandy Bridge EX, thats not set to come out until Q4 of 2011 and is set for 4P servers and up only having a 8 Core variant on the LGA2011 socket. It will also sport quad DDR3 and 2x QPI.
What you want is Sandy Bridge EN which is set for high end desktops and starter 1-2P servers. It will also be LGA2011 but have tri channel DDR3 and only 1 x QPI and is set for release in Q3 2011. Also it will only sport 6 and 8 cores while all quad core variants of Sandy Bridge (Sandy Bridge DT) will be on LGA1155 and some on the mobile part (Sandy Bridge NB).