What about Rosetta?
Office 2004 should run perfectly well through Rosetta. I still run a G4 PB, so I can't speak to this personally, but all everything I've heard seems to imply that Office running under Rosetta runs at near-equal speed to Office running on PPC.
...so, if it's speed you're concerned with, the thought seems to be don't worry too much. I imagine that's not necessarily true if you're using spreadsheets with 33,000 rows or something like that, but for relatively mild paper writing and spreadsheet use, I think the PPC version will more than suffice running under Rosetta.