it's all depend on using !
i5 is betterr for Game is Yes (since many game support 2Core ) but ... for enconding / transconding 1090T more better
Not quite. I will even up it to the 1100T:http://www.tomshardware.com/charts/x86-core-performance-comparison/compare,2761.html?prod%5B5031%5D=on&prod%5B5040%5D=on
In single core performance, a 2500K is much better than a 1100T. A 1100T compares to about a Core 2 Quad.
In some multithreaded applications the 1100T should take a lead because of the extra two cores but then again since its a Deneb core with two extra cores, the front end has to stretch the resources from 4 cores to 6 cores.
As to why its better? It overclocks better, performs better in the majority of applications most end users will use and the socket, LGA1155, will support Ivy Bridge where as AM3 will not support Bulldozer, only AM3+.