Which is better a 2.5 GHZ Phenom X4 9850 or a 3.0 GHZ Athlon X2 6000+?

Is the 2.5 GHZ Phenom X4 better or the 3.0 GHZ Athlon X2? Currently I am using the 3.0 GHZ Athlon X2 which is great, but I was wondering if the lower clocked Phenom X4 would speed up my computer because it has more cores. I mainly use my computer for productivity purposes, but I do like to play some newer games. I have heard that most games at this time can be optimized for dual core machines and they do not take advantage of the other cores on the processor, thus a faster dual core would help the game run faster. On the other hand, I have also heard that operating systems like Windows 7 can help boost the game performance by igning certain tasks to the other two available cores within the quad core processor, which will two cores that the game is running on to be more dedicated to the game. The quad core also supports the SSE 4 instruction set which is supposed to give a boost to software that supports it. Anyways, will the Phenom give me a boost on modern day applications and games because of its 4 cores or will I be better off with my higher clocked Athlon dual core. Also how does the Phenom X4 compare to the Athlon X2 when it comes to heat efficiency (I heard the quad core is actually more efficient with heat because it uses less transistors [64NM on the quad core compared to 90 NM on the dual core]. Lastly, which one is more recommendable? On one final note, my motherboard will not allow me to over clock any processor so that is not an option I have with the Phenom X4. All help would be greatly appreciated.