Phenoms are still quite capable processors . Roughly as good as a new intel dual core ... if you can overclock the phenom to around 3.5 GHz
You are in a strange situation because your hardware is all out of date so replacing a motherboard means replacing everything and its probably not worth it to do any of that ..
If this is for gaming , and if you have a 1080p monitor
Id suggest waiting . In a month or two the newer Radeon 8870 and 8850 could be good upgrades . Similarly the nVidia GTX 660 could be an option now .
Add a decent sized hard drive , or SSD as a boot drive
and a cpu cooler to get the phenom running a bit harder