Question about Gigabyte Mobo

[avaagava]

A friend of mine has an old system running at 233 mhz and was needing to upgrade the CPU as far as he can without replacing the motherboard. I'm wondering what the highest Slot 1 Pentium is that will fit in his motherboard, it's a Gigabyte GA686LX4 with 66 FSB
This is by far not my area of expertise so any helpful info would be available.

 

[Iron Woode]

According to the manual it can use 233-633 p2 and celeron cpu.

I would flash the newest bios as well.