You can easily OC the processor to around 3.4 so it'll match/surpass the stock Core 2
And the 8400 to 3.8-4.4ghz .
And even if the games soon will support quads, they wont use them even in 50% sooner than 1year. And by the time they will use it 100% the Q6600 will be old already and in need of upgrade.
So still for gaming I would pick dual core. On the other hand if you do some graphic work / editing etc go straight away for quad.
Games nowadays arent really CPU dependant - or the other way - CPUs have gone far too fast and developers cant catch up. Overclocked E2180 can handle ANY game up to date and will for next half year at least, not to mention E8400. I hardly seen my cheap
[email protected] being used more than 60% on 2 cores in games.
All you need now for gaming is beast graphic card.
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I would wait a bit if you can, if I remember correct the new CPUs / GPUs and price cuts for both are coming in just about 1month.
The 8600 will be there and they tend to clock 4.5-5ghz on air.
The 4870 1gb version will be there as well.
Prices for all of them will drop too.
Apart from that, I would consider getting crossfire ready mobo and maybe 600+ PSU.