If you compare those you would have to compare the Pentium III against the K6-III+ not the K6-II+ at the same MHZ. Even K6-III thats not + 450Mhz would have the same peformace of the Pentium III 500 Mhz. I have had quite a few of both!
In January 1999, the final iteration of the K6-x series, the 450 MHz
K6-III, was extremely competitive with Intel's top of the line chips. This chip was essentially a K6-2 with 256
kilobytes of full-speed level 2 cache integrated into the core and a better
branch prediction unit. While it matched (generally beating) the Pentium II/III in integer operations, the FPU was a non-pipelined serial design and could not compete with Intel's more advanced FPU architecture. Although
3DNow! could theoretically compensate for this weakness, few game developers made use of it, the most notable exception being
id Software's
Quake II. The AMD K6-III was unique in that it was one of the first CPUs with 3 levels of cache. The previous K6-2 utilized an off-die (motherboard) cache. With the introduction of the on-die L2 cache, AMD designed the K6-III to also incorporate the motherboard's pipeline cache to boast an L1, L2 and L3 cache."
"Throughout its lifetime, the
K6 processor came close, but never equalled the performance of processor offerings from Intel. While there were brief periods when AMD announced a clock speed advantage, volume availability of products was limited as AMD suffered from manufacturing and yield problems. Furthermore, having deviated from the official Intel motherboard specifications with the
Super Socket 7 format, the motherboards that worked with the K6 were of varying quality, especially in regards to their implementation of the graphical
AGP specification.
Overall the K6 proved popular with consumers, especially in markets outside North America, offering decent performance and a comparatively low price. But the problems surrounding the platform, and lack of availability for the announced high end parts, failed to establish AMD as a player in the corporate market. Intel responded to AMD's lower prices with the lower budget "Celeron" version of their Pentiums. While the Celerons were not as popular as Intel had hoped, this effectively left AMD struggling with low margins, chasing the low end of the market."
http://en.wikipedia.org/wiki/AMD#K5
