Try using the Function - F2 (FN-F2) key combo to see if it will change the mode.
After, doing a little reading around... there are a few Toshiba owners of the L50 and L55 who had the same problem after the Bios update to version 2.00.
I did not see any details on how they did it, but, a couple stated they re-flashed the bios and one down-flashed his bios. They stated it fixed the problem of the cpu running at .798 with a 2x or 3x multiplier and restored the correct CPU multiplier & speed; also, gave them all three options for the Dynamic CPU Frequency mode (SpeedStep).
Dynamically Switchable (default) - The Power Saver controls the frequency.
Always High - Accelerates the CPU
Always Low - CPU normally uses this state
Remember, you flash the firmware at your own risk.
Good luck, whatever you decide to do.
If I were you... I would email or call Toshiba support and get their advice, too.
EDIT: I found a thread at the Toshiba forums where a poster stated, you could only downgrade using the ISO file, in the firmware download. He mentioned booting from a CD with it. You could not downgrade from the Windows firmware utility.