Just some benchmark values from the machines I've been running MemTest86 on.

First box is a Pentium III 550Mhz with (I believe) PC100 memory (MemTest86 reports it as a 568Mhz CPU). L1 cache (32Kb) speed is 5567 MB/s, L2 cache (128K) speed is 2523 Mb/s, and main memory clocks in at 198 MB/s.

Second box is my Athlon XP 2600+ with GeIL DDR-333 (PC2700) ram in a 2x512Mb configuration. CPU speed is reported as 2088Mhz, L1 cache (128Kb) speed is 12808 Mb/s and main memory speed is 1182 MB/s. This is the box with what I believe was the bad memory stick, so I've got both sticks in and I'm going to run tests overnight. (Found errors after 1 hour, pulled the "good" module and left the suspected "bad" module in. Memory speed is now reported as 734 MB/s since the DDR isn't active. A single test-pass of 512Mb, using the default set of tests, takes around 30-35 minutes on this machine.)

BTW, MemTest86 is a sweet little program. If your machine can boot from CD-ROM (most can if they were made in the last few years), there's an ISO that you can download and create a bootable CD. Pop the CD in, power-up and MemTest86 will automatically start running the default tests. I ended up using an 8cm mini-CD since the ISO is only 16Mb or so. Only disadvantage of the tiny size is that I can't use it in a side-ways mounted CD-ROM drive (no clips to hold it in place, tray has to be horizontal). Also, once MemTest86 starts, you can remove the CD-ROM and go boot it in another PC.