Well I think that there are two options/opinions for everyone here..
Option One
There is currently nothing on the market (except SupCom) that really needs more than a decent dual core, so for now a decent dual core will do you fine.
They are cheaper and will last you into Q4 2009, so for all the foreseeable releases.
Option two
A quad core offers much more future proofing. If we look at both Intel and AMD's roadmaps then we can see that it is cores, revisions, cores, revisions, cores and I dare say this trend will continue till we hit the 16 mark and that means two cores will not cut the mustard in the future. Although yes the 6600 is not a native quad, it still offers more ability to cope with multicore loads than dual
A key factor to remember before I ramble on though is that the PC is designed to do a lot more than just play games.
The market
What it appears to comes down to, is that it is not just Intel and AMD, but Sony and Microsoft that we need to consider too now (forgetting Nintendo because they have obviously gone mad now).
So if you can please bare with me here then I think you will agree that console games are built for mulitcore games, but the console multicore is not the same multi as a PC multicore! In the development sense they are infact completely different and by looking at current console to PC titles this doesn't appear to transpose very well to the PC market.
It seems 'most' developers are having a lot of trouble working out load for the various cores on consoles and are finding things even harder due to the fact that EVERY platform has a different base at the machinecode level, but consoles it seems is now where the majority of developers begin.
The oh familiar phrase from the doom mongering console fanboys this year has been that the PC games platform is dead and although this definately not true, the cries have been stired from the actions taken at high levels in the games development industry ordering that games companies look to the 'casual gamer' which they see as a way to make the real money. So we are seeing more and more console games developed first whilst we see less PC exclusives being developed for its the PC platform.
Listening to interviews shows us that developers WANT or would prefer to build games on the PC. They are traditional, offer a lot more power and are easier to build games for, but that just isn't an option that most developers are given anymore.
So yes we will see games being developed for PC exclusives (or as exclusive as 'EXCLUSIVE' is these days), but these are really only going to be from flagship developers who can throw a lot into building games on this platform as as such you can bet your ass they will need the latest hardware to run them.
Developers are learning how to transport code from a console to a PC but because consoles hardware only cycles onces every two years, so they can work the market (so to speak) then the PC owners can expect to own hardware that is vastly more powerful than the specifications for its software; with the exception of those flagship titles or those games (like GTA) that are badly ported.
The question
I personally made my decision by purchasing a Q9550 last week, however I would suggest waiting if you currently have a decent dual because there just isn't anything that is being developed that will need it. With a cheap quad you will get some good speeds (more than a quad) out of it, but process speed it seems is not what will matter so much for the close future, it seems that software is going to be more about load management and process revision or at least until whilst developers learn how to handle this curveball that is the console.
.
