Eventually I left the FSB at 200 and set the CPU multiplier to 13.5 which came close to the rating of 2.8 Ghz, but more like 2.7 Ghz.
BIOS. Not easy to do entirely in Linux. You download the *.exe file needed, in my case it was the F7 BIOS version needed in order to recognize the Sempron 145 CPU. It's a self executing zip file for windows, so change the file ending to *.zip and then extract the MA######.F7 file. There are 3 files in the zip, one is autoexec.bat to run in windows, the other is an exe file to run in DOS or windows and the third is the actual BIOS program. Put that file in root folder of a drive, I used a FAT32 drive partition just in case. You can then use the Qflash program in the BIOS instead of the DOS based flash utility to access and install the new BIOS program file, the one with the *.F7 ending (or whichever version you needed).