After having to replace my motherboard, my computer is registering my cpu as an athlon 2000 instead of the athlon 2600, obviously the shop that installed it didn't optimize the settings. I had to change the front side bus from 100 to 133 to get it to the latest speed, there must be other things in the bios that I will need to change to get the full potential of my cpu again.
My motherboard definitely supports the 2600.

There are several different versions of the 2600+, the 133MHz(266FSB) version is probably the worst of the bunch. Without giving the make/model of the board & the type/speed of RAM you have, no one can really tell you what BIOS settings will work best. But default settings are almost never the best performance settings.

You can change the multiplier too... also the bus can be 166 or 200...