1. The two CPUs are in radically different price ranges and yet you do not tell us what price you want to pay? What is your budget? Gaming resolution? What video card are you planning to pair with the new CPU?
2. read this in order to give us enough information to help more than I try below:http://www.tomshardware.com/forum/261222-31-build-advice
If you are looking for a quick answer though:
The phenom II 925 will be enough if you don't plan on getting something big like a radeon 5850 or higher. Overclocked, it will be fine for even a GTX480. Dual cards you might want to look into something a bit higher end, ie the i5 or phenom IIx4 955/965. triple cards you will be wanting an i7 or perhaps could settle for a phenom IIx6 1090t.
If you are debating between these two CPUs because you think they are about equal, your information is outdated. The phenom II was about as good as a core 2 quad at 0.2GHz faster. But you are talking about the icore series, not the core series. The difference is more like 0.8GHz for equal performance.
Here's a good link where you can view benchmarks of various modern processors for comparison in performance:http://www.anandtech.com/bench/Product/109?vs=81
Good luck with whatever your decision is and feel free to ask for more specific advice if you need it