Getting back to your question - I'd recommend the FC-PGA format over the Slot 1/SECC2 format, because it is more versatile. All you need to make it work in your Slot 1 board is a 'slocket' (socket 370 to slot 1) adapter for FC-PGA, which are readily available. Intel is switching over to FC-PGA, so why go backwards. Besides a lot of newer mobos are Socket 370 now and won't take an SECC2 no way, of course.
Get a cB0 FC-PGA P3, a slocket, a good HSF and some primo PC133 CAS2 SDRAM and you would be set.
You may want or need to upgrade your board's BIOS for the P3 CPU. The newer BF6's have SoftMenu III and the latest BIOS is dated 7/3/00 !!