http://home.thezone.net/~bm/benchmarks.html
Comparison using Q3Test of AMD K6-2 400 vs K6-3 400 vs TNT 1 vs G400 using latest and fastest OGL beta ICD.
I had a system in to be looked at so I used the parts to test in my system.
Short:
K6-3 400 30-40% faster than K6-2 400
G400 200% faster than TNT 1 above 1024x768
TNT 1 faster than G400 (at max like speeds) below 1024x768.
Comparison using Q3Test of AMD K6-2 400 vs K6-3 400 vs TNT 1 vs G400 using latest and fastest OGL beta ICD.
I had a system in to be looked at so I used the parts to test in my system.

Short:
K6-3 400 30-40% faster than K6-2 400
G400 200% faster than TNT 1 above 1024x768
TNT 1 faster than G400 (at max like speeds) below 1024x768.