My vote goes for the x6.
LGA1156 was dead the moment it was introduced. Disagree? Show me a roadmap with future product releases for LGA1156.
AMD will support AM3 with future processors. AM3+ chips should drop right into the AM3 socket. Sure, wont get full AM3+ performance, but you'll get a good boost none the less.
Besided, you're still running a single core 3500 right? Having six cores will make multi tasking so much nicer.
And honestly when gaming, you're not going to see a huge difference between the x6 and the i5 in day to day performance. Go with the platform that'll last you the longest, including future CPU upgrades. Only Socket AM3 can offer you that.