I think you should use your P3V4X, which is an
AnandTech Editor's Choice. You just have to update the BIOS for the board at the
ASUS P3V4X web page by following their directions. The new BIOS will recognize the newer faster CPU's.
Since you are not going to overclock, I'd recommend you get a P3 designed for the 133 MHz system bus, like the 800EB or the 900, instead of the 850, which is designed for a 100 MHz bus. Also get the CPU in the FC-PGA (flip-chip) form. Then get an ASUS S370-133 "slocket" to use the flip-chip in your Slot-1 board ($20 at
CompuCheap). You can use the stock fan that comes with the CPU you buy or, if you want to get crazy, replace it with a GlobalWIN FOP32-1 cooler (also $20 at
CompuCheap). All this should work with your ASUS board.
I did something like this recently and it only took about an hour to put it all together once the parts arrived.
For more info on P3 CPU's see
this.