Há uma descrição em HowStuffWorks ,
The smaller L2 cache size and slower bus speeds can mean serious performance differences depending on what you want to do with your computer. If all you do is check e-mail and browse the Web, the Celeron is fine, and the price difference can save you a lot of money. If you want the fastest machine you can buy, then you need to go with the Pentium 4 to get the highest clock speeds and the fastest system bus.
Isso implica que, se você quiser poder de processamento, o cache, a velocidade do clock e o desempenho do barramento serão importantes. Mas, para uma máquina básica de internet, o Celeron seria uma boa escolha.
Mais informações detalhadas neste artigo do TomsHardware 2002 que discute o Celeron com base na arquitetura P4 .
The low-cost processor now enjoys all the advantages that had previously been reserved for the P4. This includes the same large selection of chipsets and motherboards, and all the technological features - including the fast clock speeds that have proven to boost sales considerably. And the fact that more chips are being produced will also reduce the prices of all the surrounding components.
Este artigo compara os dois processadores (em 2002) e apresenta alguns resultados de benchmark.