Have a Gigabyte GA-MA770-DS3 motherboard (AM2+), with Athlon 64 X2 5000 B. Edition on it,
would like to now what is the fastest CPU I can install on this MOBO.
BIOS updates arent always a sure thing....The 9850 will do just fine but For the price i say get this: http://www.geeks.com/details.asp?invtid=HDZ940XCJ4DGI-BP&cat=CPU
Your link directs at the AMD Phenom II X4 940 which is not supported according to the gigabyte supported cpu list.
And the 9850 from that site is the 125W version which is also not in the supported cpu list.
So you need to be looking out (fastest for the board) for a Phenom X4 9850 95W