The Slot-1 P3's are based on the Katmai core that has 512KB of cache running at half the clock speed of the core, and it is on the PCB that the CPU is sitting on.
The FC-PGA P3's are based on the Coppermine core, that has 256KB of "on-die" (read:cpu speed) cache that run at the full speed of the CPU.
The Slot-1 cpu's run waaaaaaaaaaaaaaay slower than their FC-PGA counterparts because of the latency and slower speed of the external cache. Unless you are given a *SWEET* deal on the old Slot-1 processor, I would shy away from the Slot-1 processors.
Although, some newer (533MHz and up?????) P3's are Coppermine processors dumped on a Slot-1 card. If you have the mobo to support it, they aren't a bad deal.
If you buy a Slot-1, just make sure you get one with a Coppermine core and not a Katmai core, and you should be OK.
If I am wrong, feel free to flame away!
