Might as well get this one... and make your quad an "Official" hex-core:
http://www.provantage.com/intel-bx80613w3680~7ITEP374.htm
what is the difference besides like .1ghz
Do the comparison at Intel's website. Besides .13 gHz, the 3680 has much greater QPI speed (6.4 v. 4.8) for the same price, and is a well tested CPU with tons of benchmarks. Why would you go for a slower anything when upgrading, aside from budget or reliability? The 3680 offers the best of both.
By that logic the 3.46Ghz W3690 would be better.
The big difference is price. Provantage seem to be the cheapest and have them priced as follows:
W3670: $587
W3680: $590.5
W3690: $1048.68
http://www.provantage.com/intel-bx80613w3680~7ITEP374.htm
By that logic the 3.46Ghz W3690 would be better.