The i5 is the best thing you can spend your money on and second place is the p2 x6. Both are very good and for raw power the x6 can beat the i5 when overclocked but your apps will have be well threaded to make the best use of it. The i5 has the best memory controller, performance per watt, performance per clock, and lower power consumption. Overall the i5 is the best all around cpu you can buy for just about any thing.
tbh there isnt a comparable amd processor to the i5 especially if u meant the 2500k
the x6 would be the same or slighly better at really heavily threaded applications while the i5 excels in pretty much everything else
If you are using programs that can make use of all the cores in the the FX 8150 like video encoding then the FX will be faster. Any programs that can use at most 4 cores the i5-2500 will win.
Most games only use 2 cores so even an i3-2100 can perform better at least just as well as an AMD CPU. Mafia 2 is one of those few games that can use 4 cores, however an i3-2100 can equal a Phenom II X4 980 in frame rate benchmarks.