Eh. Tough call.
I'd probably keep the FX, despite the i3 probably offering more performance in a lot of games, because socket AM3+ is newer than socket 1156. 1156 is around 8 years old and stopped seeing new designs in maybe 2010, whereas AM3+ as received new CPU designs as recently as 2012.
On the other hand, you can drop in an i7 8xx into an 1156 socket, which will be faster in games than any AMD CPU, period.