Im planning to buy A10 7850k

That Pentium can OC easily to 4.2-4.4GHz and is better in just about every game than Quad cored Athlon x4 and A10 (not with integrated graphics, ofcourse). CPU performance wise, its the best value for money and i3 comes next, it competes with FX 6. Intel has alot better single core performance, you'll need to buy high speed memory and a good OCing board with that A10, and even with OC, it won't beat Pentium in single core performance (or maybe just very slightly).

Games still rely heavily on single thread performance, and just because A10 has 4 logical cores doesn't make it a perfect quad core. It has those cores in an arrangement of 2 cores per module and 2 such modules, hence less single core performance and less FPU than Intel, as AMD's 2 cores share the same resources vs different resources for each core in Intel, which follows the 1 core per module standard.

Best of all, you can OC the Pentium on a $60 H MoBo which'll save you bucks for a better GPU, and 750 Ti is ALOT better than A10's integrated graphics. You'll need very high speed memory as APU's integrated GPU relies on that for memory and you'll need a very fast (which's expensive, of course) memory. Keeping all that in mind, Pentium is a better option, when paired with 750 Ti.

And actually your MoBo supports PCIe2.0 which's no different from current 3.0 in terms of real performance, you can just put in a 750 Ti there which'll increase performance by alot.

APUs for gamers (not casual) is not recommended, a Pentium+GPU combo takes on quad core Athlon (better than APU in OCing, it requires very good CPU cooler)+same GPU head on, and usually wins.

An APU like A10 will require fast memroy+good OCing MoBo+good CPU cooler to be able to match up with Pentium+cheap H MoBo+normal memory+af cooler's perforamnce. A better value/money and a better buy overall.

Or even better, just buy yourself a new GPU, like 750 Ti and you're set for high-ultra gaming, I know your CPU is not the best clock speed wise, but believe me, Intel are much better than AMD in this dept. A 3.2GHz i3 will defeat 4GHz FX 8 in single core performance. Yes, C2D will not match up Pentium's performance.