I have an elderly G4 Power Mac (specs below). I'd like to add additional RAM, but I'm having trouble finding the 2600 speed. Doing a little research I've found that 2700 works for the 1.25 Ghz machines, but is it compatible with the 1.0 Ghz? If not, should I replace the 2600 with the PC2100 when I add more?

Dual 1 GHZ PowerPC G4 1 MB L3 Cache per processor
512 MB DDR SDRAM PC2600U-25330