Macworld posted benchmark results for Office 2008. Be sure to read From the Lab: Measuring Office 2008's performance
Overall Office 2008 scored higher results on an Intel Mac. PowerPC-based machines are in for more of a mixed bag, but Entourage did score higher on the PPC. Machines used: 4-core, 2.5GHz Power Mac G5 and a four-core, 2.66GHz Mac Pro. Both machines ran OS X 10.5.1 and had 2GB of RAM.
Even on my lowly G4 Dual 1.42 GHZ, Memory 2GB, Mac OS X 10.5.1 I see some slight increase in speed.
