Upgrading from e6400

I'd go for the e8200 ($99.95 at microcenter) if they still have any in stock. The q6600 only runs at 2400, so unless you overclock it, it won't be any faster than your current cpu. The e8200 is a better value if microcenter still has any left.

The ASUS P5W DH Deluxe CPU support page shows that the Q6600 is supported but it looks like any 45nm or 1333FSB CPU will have only limited support due to chip set limitations.

Digging around the FAQ, I found the previously noted CPU feature limitations and also this answer to a poster running a E8300 well (but without Speed Step):

The way I see it, you've got three problems; mobo chipset limitations, 65nm CPU (runs hotter than 45nm), and only 2MB of L2 cache. On the plus side, a Dual Core CPU generates less heat than a Quad Core one.

Personally, with a P965 mobo myself, I recently chose the E8200 for $99 at MicroCenter option as an upgrade to my E6400 to get a cooler-running 45nm CPU (for overclocking) and 6MB of L2 cache. With the same 8x CPU multiplier as the E6400 I'd get the same CPU frequency at default 1066MHz FSB or a quasi-overclock at 1333MHz FSB or a cooler 50% overclock at 1600Mhz FSB.

In your case though, the switch to a Wolfdale CPU comes with significant strings attached. Meanwhile, switching to another Conroe CPU won't likely provide any great benefit. For media encoding apps that are able to utilize it's four cores, a Kentsfield Q6600 (B3 or G0 stepping - not sure which is better) provides 8MB of L2 cache (2 x 4MB) on a 1066Mhz default FSB with a 9x CPU multiplier. Up to you if the ~$200 price is worth it. In the USA, used E6400's are selling for $75-100 on eBay so factor that $$ into your cost calculations.

The E6850 for $126 suggestion seems a little absurd in that it's a 1333MHz FSB CPU while still being only a Dual Core, 65nm chip. With only the same 9x CPU multiplier as the Q6600, it seems to me that you'd be loosing more with a E6850 than you stand to gain with a Q6600.

Personally, in your shoes I think I'd buy myself a new mouse and stop the upgrade there while waiting to see what the upcoming Lynnfield LGA1156 CPU's look like.

Regards.

The Asus with a 65nm proc (specifically the e6850 being fully supported on the Asus CPU support list), for whatever reason, is capable of running a 333MHz FSB.

Quite frankly, 9x400MHz FSB is easily within reach and would bring him in at 3.6GHz, run his RAMs synchronously if he has DDR2 800, and run comparably to the 45nm e8400 at the same clock speed.

And cost $75 less than the Q6600 (which the OP clearly does not need).