I checked the AMD website and your board can stay still on the same case by installing a Phenom IIX6 1100T(HDE00ZFBK6DGR),3.3GHz,125W,rev.E0,SocketAM3,6-Core
I am doing a build myself and I discarded the I7 from Intel simply because I am not calculating an orbit, I do not work on a Black Mesa Research Facility, Gaming is not THAT important and I am not trying to decypher the Human Genome.
So I decided to Buy a AMD+ with 8 cores. Because gaming is that important. Not I7 important. also... the price of an I7 is the price of excellent sound card or more storage capacity, or a monitor or something + something else.
If you will benefit from 6 cores (usually with content creation) then the x6 is a good upgrade, otherwise I would not upgrade. You have a fast CPU for a Phenom ii. I would not upgrade to Bulldozer, however, as in many cases performance is the same, if not worse than a Phenom ii x4. If you switch to Intel, you will need to get an i5 to see a noticeable performance improvement, the i3 and Phenom ii x4 are neck and neck.