Intel’s quad-core desktop Penryn CPU Core 2 Extreme QX9650 (Yorkfield) has been available to a couple hardware sites and their reviews got published today.

The Intel Core 2 Extreme QX9650 is the first 45nm desktop processor that Intel will be launching in a couple of weeks.
Highlights of the new Intel QX9650 CPU include better performance, lower power consumption, new high-k metal gate transistors, additional cache and SSE4 instructions set support.
Intel Core 2 Extreme QX9650 Review Round-up:
Hothardware
Techgage
Techreport
Firingsquad
Tweaknews
MadShrimps
ExtremeTech

Overall the new 45nm Intel CPU gets a very positive review. If it will be worthwhile to upgrade to the Intel Core 2 Extreme QX9650 is now depending on its price. Intel is expected to reveal the price in about 2 weeks.