I must stress the fact that a CPU is VERY important in games, slightly less important in most games then the graphics processing unit in your graphics card, however it is still extremely important.
You are talking about an AMD 3700+, if this is indeed the case then you have posted this thread in the incorrect section i.e. the Intel Section
If you had the option to take a Core 2 Duo over a 3700+ you should always take that option as the architecture is far more sophisticated and "powerful" than AMD's current architecture for the AMD64/X2. Even in single threading mode the architecture is far more efficient and effective at dealing and processing single threaded information than the K8 architecture. This is noticed a lot in tests that use large amounts of SIMD extensions i.e. SSE-SSE4. Also Core 2 Duo incorporates SSE3+ (SSE4) which allows an increase in processing SIMD instructions with its new set of sub-code.
Now bottlenecking. Itâ€™s different from what you have made out. First I will say that an AMD 3700+ would bottleneck your system in some cases and not in others. You can't just say will my processor bottleneck my graphics card? Because there is no correct simple yes or no answer that could be given to that question.
Letâ€™s use two examples here:
Doom 3 at 1600x1200 @ Maximum Settings, 4xSSAA. Your processor will bottleneck this application and a reduced frame rate will be noticed.
Red Alert 2 at 1600x1200 @ Maximum Settings. Your processor will not bottleneck this application, maximum frame rate will be obtained.
So the answer is you will notice or not notice bottleneck per application you run, they all have different requirements but if you intend to play games like Doom 3, Crysis etc then yes you will receive a CPU based bottleneck on these applications depending on system configuration and graphics/processing options set in the game.
As for DX10, yes if you get that processor you will have wasted money in a way. It will still be fast, but DX10 is built around the ability to use multithreading data i.e. Two processors or greater to process information. Therefore single core processors will not be able to work with DX10 extremely well in comparison to a system running SMP Multithreading