Worth upgrading CPU

I'll give you the short version. I have an m2n32-SLI Deluxe MOBO. Nforce 590a sli. System Bus 2000/1600MT/s, PCI x16 that run X16 mode in each slot, good power supply to support nearly any video card or cpu.

Asus has been painfully slow in creating drivers to support new Phenom II Cpu chips on this board but recent bios revisions lead me to believe they are close to releasing a bios to support them. My question is if it is worth putting a Phenom II chip in this older AM2 board. Will the slower bus speed cripple it? Are my PCi-E slots going to bottleneck me. I mostly game on my computer but would love to benefit from the performance increase of a quad core for encoding. My thinking is that I could upgrade my CPU and use saved money for better video card but, will the performance increase really been seen on my older board or am I going to be paying full price for only half the performance increase?