Upgrating 2year old MB with newer CPU: warning from Gigabyte website

Hi,
I have a GA-M61SME-S2 motherboard.

I would like to upgrade the CPU on it with a :

AMD Phenom II X4 940 Deneb 3.0GHz 4 x 512KB L2 Cache 6MB L3 Cache Socket AM2+ 125W Quad-Core Black Edition Processor - Retail

I went on the Gigabyte website to see the list of supported CPU:
http://www.gigabyte.us/Support/Mot [...] #anchor_os

It is supported, but with the following warning:
*Note: If you install AMD AM2+ CPU on AM2 motherbord, the system bus speed will downgrade from HT3.0(5200MHz) to HT1.0(2000 MT/s) spec; however, the frequency of AM2+ CPU will not be impacted. Please refer "CPU Support List" for more information.

What does this mean? Am I better off with the fastest AM2 socket CPU that doesn't cause this system bus speed to slow down? What is the 'bus speed' anyway?

Thanks!
Dave