I've just converted an old Dell Dimension 4400 to be used as a server (dropped in a SATA PCI card and added a few drives and maxed it out with 1GB DDR ram).
Its old chip was a Pentium 4 1.6ghz (Williamette) that runs with 256kb cache.
I have another old Intel system that I just ripped out and replaced. It's ATX so it won't go in the BTX 4400 case (shame) but I did try the 3.0ghz P4 Hyperthreading CPU in the Dell.
It booted straight up but because the 4400 is limited to 400 FSB the CPU only runs at half speed (1.5ghz) - 0.1ghz less than the original chip.
It does, however, have 512kb cache and it's "dual core", "Hyperthreading" etc. Although the 4400 Ram is single channel.
My question is ... which CPU should I run with?
Is double the cache and hyperthreading a good trade-off for the 0.1ghz cpu speed hit?
Will the new CPU run cooler as it's not being maxed out?
As just a home server either CPU would be fine.
Any performance difference would be hard to detect in any normal home server usage.
CPU temps should also be not a factor. It will be 'cool enough'
It's probably not worth your time or trouble to swap CPUs in any case.