You can't really get a whole lot more performance with that motherboard. There are no adapters to run anything other than a Socket 7 CPU in your board.
A K6-2+ or K6-3+ could boost performance some, but they will only work with the earlier P5A. They won't work with rev. 1.05 or later.
If you have the early version of the board, and picked a a K6-2+ 550 for less than $30.00, that'd be a worthwhile upgrade. But that is pretty unlikely.
In my opinion, you'd be better off saving your money and making the jump to a Socket A based system, with DDR ram, and an ATA100 harddrive.