Hmm, a lot of confused people here.
First, a celeron 500 vs a p3 500 is not actually that much slower. Yes, it does *only* have 128kb of L2 cache ram, but that ram runs at full processor speed. The original P3s cache only ran at half speed. Also, the bus being limited to 66 Mhz does hamper performance, but at only 500 Mhz the difference is not huge.
The real fun comes when you overclock the celeron, if you get a good one to run at 100 Mhz FSB you will find that it's performance is identical (or even better) than the p3.
The situation is different for the faster celerons. Once they got to 700 Mhz + that 66 mhz bus was really holding their performance down. It would be a safe bet that a 566 Celeron would perform (and often outperform) the early Katimi core P3s.
As for video cards, current CPUs are WAY WAY WAY WAY WAY (add 5 more ways) overpowered for the current generation of cards. All of today's video cards are limited by their RAM. Ram speed, unlike processor speed, has not advanced as rapidly. Any CPU above about 750 Mhz or so can easily fill rate limit even a GF 2 Ultra at high resolutions. (I'm not talking about the amount of ram, I'm talking about the speed of the ram.) I believe the GF 2 is advertised to have a peak fill rate of something like 1 Gigatexels, however current ram limitations limit it to about 300 - 500 Megatexels.
This is pretty easy to spot in game benchmarks for new CPUs. Often times the tests will be within 1 fps of each other, this is because the video card just won't allow any higher framerates.
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bloom25
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THUNDERBIRDS