Okay, I am building my New computer, and have yet to buy the motherboard and CPU yet. I am choosing between these CPUs:
Phenom 9600 BE
Athlon X2 6400+ (maybe to hold out for better Phenoms)
Now, this is where my situation differs. My computer will be used probably 85% of the time for general use like internet, homework, forums, ect. Then like 10% gaming and 5% rendering/programming work. So, I was thinking that I am going to need overall CPU horsepower for my situation, so maybe the Quad Core would be better than the Dual Core E8400. But the E8400 can go to 4.0Ghz which is amazing, and will give great performance, but a 3.4Ghz Q6600 will also give some amazing performance because of the four cores.
Internet, homework, forums etc don't require much of a CPU at all.
A cheap Celeron or Sempron would do fine here.
Gaming, the E8400 is the way to go.
Rendering/Programming, it really depends on the application.
A quad core would generally be the best here, but then you are not doing this very often, and most applications as of right now don't really use a quad core all that effectively even if they have multiple CPU support. I don't think you would see a huge improvement over a fast dual core.
My 2 cents, get the E8400.
I myself an probably the type of person that the quad core is built for... I never do just one thing at a time. I like to download things, check e-mails, run upgrades, etc. The machine I have came with the quad core... and with the 4Gb of ram I have... it really can handle anything I put it through. It may not need all that power... but it is really nice. My laptop on the other hand is a dual core... man there really is a huge difference to what I can handle... since it would also give you longevity... stick with the quad... you can't go wrong.
Dear god, go for the Q6600. Games do rely on the CPU quite a bit more than some would insinuate, and the moment you think "multitasking" the next thought in your head should be "quad-core". Even though games are supposedly not built for quad cores yet, quite a few end up utilizing multiple cores.
I've used single core, dual core, quad core, and octo-core setups (two processors), and I can easily say that the quad core is the best of the bunch, even in a mid-sized budget. Dual core setups do work quite well, but once you go quad-core, you'll never want to go back.
I'm not sure when the quadcore became the defacto standard for multitasking. I've done some serious multitasking on my Pentium D 805 and have never felt bottlenecked. Usual multitasking scenario is a multithreaded video encode taking about 90% cpu usage on both cores while doing word and firefox with the remaining 10%. The most extreme multitasking session I ever had was when I did a batch encode of videos from wmv to 3gp format using a single threaded program, while playing Call of Duty online at the same time on the other CPU core. I was at 100% usage on both cores for 4 hours straight. In the days that I used to run the software TV capture card on my pentium d rig, I would routinely capture video into mpeg2 (60% of one core) while surfing the web and watching flash video online (90% cpu usage of the other core).
Now I'm sure that some people can bottleneck of dual core cpu with their multitasking. I'm just giving examples of my multitasking experiences as a measure of what even the crappiest dual core can do.
Any of the CPUs you've chosen are good. If you lived close to a Microcenter, I'd say buy one the Q6600 they have for $199.
Do you really need to upgrade right now? It sounds like you are only playing games and doing programming stuff once in a while. Maybe it would be better if you used your current rig (until it dies), sell the working parts, and then get a newer system (ex. Nehalem, when it comes out). If you think your specs are low, just look at mine (below). Honestly, I don't know where some of these upgrade fanatics get the money to pay for all of this hardware. Don't any of you guys actually use your pc's until they break?