since you are thinking of changing your platform, as much as the i3 2100 is a good budget chip, it really wouldn't hold up against your 1045T*. an i5 2300 would give you a slight increase.
not to throw out the i3 option; the 2120 would give a closer performance for a reasonable price difference and at significant lower power than the 1045T or i5. if you are able to put an i3 on a z68 chipset and add a ssd for caching, you will most likely enjoy the results.
* edit - that is incorrect, my bad:http://www.tomshardware.com/reviews/gaming-fx-pentium-apu-benchmark,3120-3.html
the i3 2100 holds its own on that and the preceding pages . . .