new system or used? there is no guarantee of a successful unlock one or both cores may be defective. the g3260 has a better single core performance, multicore performance and a lower power draw. the Phenom ii is an old chip (I have a 955black) the g3260 is much newer. this will be the last CPU (AM3) you put on that motherboard as you can only buy used CPU's for that platform. the G3260 can be further upgraded via a bevy of different chips.
this seems to be a no brainer if the price is similar.