I have quite a bunch of AMD Socket 7 CPUs around, from the humble K5 to the latest K6-III+ versions produced. So yesterday I made a little test with 2 CPUs I clocked at 500MHz to compare the 3DMark 2001 SE results on my system.
The first contender is a K6-2+ 500 (really a 550 downclocked), which is the low-power (0.18 micron, 2.0V) variant of the K6-III core with only 128KB L2 cache as you can see on the CPU-Z screenshot.
The second chip is a K6-III+ 500, which is the same chip but with the full 256KB of L2 cache, this one runs at an even lower 1.8V.
Running 3DMark 2001 SE gives us 1900 points on the K6-2+ and 2016 points on the K6-III+, which is a 6% increase only die to the aditionnal 128KB of L2 cache. This is of course only one benchmark which also takes into account graphics, but it gives us a good idea of the performance increase between the 2 “high end” cores produced at the end of the K6 family life.