If you plan to get the Q9450, get it, as supplies are limited for some reason. The mobo you paired should be able to support it natively, there has been really good reviews on the P5Q-Deluxe (p45 chipset).
You forgot the 4th law of gravity on the quantum physics line 20 section b that states if there is two 0's it multiplies the multi threadulature by 100 so it would be 4800+= 12 x 100 which = a whopping 1200!. (/sarcasm off)
Just bought q9450 and Asus Maximus Formula, ddr2 4 gb (800mhz)+ 8800gts Alpha dog version and after upgrading the bios on the MB i works like a charm, OC it to 3.0 Ghz and i runs cool and absolutely rock solid.. Perfect for my use(gaming mostly FPS and officework)
Thumbs up from me, ddr3 are overrated.. but in the future they will rock if they dont find something new ..like ddr5..
I have a Q9450 and I like it a lot. However, what will you be doing with your computer?
If it is primarily for gaming, then I recommend the E8400 which runs at 3.0GHz. Nearly all games right now that "uses" multi-core processors are not optimized yet. It will take a while longer for games to be optimized for Quad Cores.
If you do multimedia stuff (specifically video), then by all means buy the Q9450.
DDR3 is too expensive for the little performance boost you get. Unless you care about synthetic benchmark numbers, you will not notice any performance difference. Want more performance dump DDR3 for DDR2 and use that money for a faster CPU.
I was going to be gaming. Warcraft, Age of Conan etc....I figured from I read I knew it was going to be a little slower gaming (right now) but eventually may find its way to the top of the list when gaming starts to include the extra cores.