the i7 is theoretically better, tis a new technology, hence why it costs more, and can be faster that the p8700 with turbo boost. has the memory controller onboard, new architecture etc...
The i7 is newer and it's a Quad Core. It's only runs at 1.6Ghz when there 4 cores working and then it's probally at 1.73Ghz most of the time. When there is 2 thread it runs at 2.4Ghz (just behind the P8700) and with 1 thread it's at 2.8, so quicker.
I'm sure the i7 would be faster in other area's like DDR3 and so on.