Only the 1.42 ghz came with a copper heat sink.

A dual 125 or 1.42 will be faster as not only are the processors faster, they also have a larger cache. If you get a 1.42 then it might be a good idea to score one with the heat sink.

When you installed the dual 1ghz, I hope you altered the motherboards bus speed resistors. If not then your 1ghz processors are likely running very slowly