You could buy phenom 2 550 and unlock the cores and that would be equivalent to a quad core processor almost the same as phenom 2 955. The only caveat is, it might not unlock as the cores could actually be bad. With a good batch, chances would be high though.
For gaming cache is very important, therefore p2 550 might be a better choice. For vmware quad core would be a better option as you would be able to run more virtual machines. Power consumption of A2 620 would be better compared to a p2 550 unlocked, so athlon might be better for 24/7 operation, p2 550 without unlock would be consume less power though.
gigabyte mobo would be able to unlock 550 without any problem.
If you can't get a good batch, I would personally prefer A2 620 overclocked to 3.5GHZ

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