Backup Machine - processor Upgrade

I am trying to upgrade my old trusty Dell Optiplex GX1 400-L (Low profile chassis) backup machine, running W2000, for when my main machine breaks down (like now, for instance - am using it at the moment...)

This Specifications page at the Dell website says that the Optiplex GX1 processor speeds vary:
Documentation

..from: 266, 333, 350, 400, or 450 MHz (Pentium II);
to: 450, 500, 550, or 600 MHz (Pentium III)

I have had the 400MHz (Pentium II) for donkey's years but have just bought a 600MHz (Pentium III) Cpu and heatsink on Ebay and I am wondering if I am doing the right thing?


The Optiplex GX1 Service Manual also gives a series of settings for the System-Board Jumpers in increments from 266MHz to only 500MHz and I am also confused about:

"Install 500MHz jumper if the microprocessor’s internal speed is 500 MHz; otherwise, the jumper should not be installed"
"Install 450MHz jumper if the..." etc, etc down to 266MHz.

..and also: "One set of speed jumpers must have a jumper plug installed; otherwise, the system defaults to 350 MHz."

The confusing thing here being the jumper setting currently is 266MHz!


I am also wondering on the maximum sensible Mb to go up to on a Graphics pci Card - The current onboard Video Memory is just the standard 4mb with a further (unobtainable) 4mb uprade option - the PSU is only 145W
I dipped into Ebay and am waiting delivery of an 8mb Matrox but I'm wondering if I could have gone for something a little stronger?

Many thanks in advance