I am currently running a 15" imac, 800MHz, G4, with 1024 MB memory.

I am considering upgrading to a 15" powerbook, 1.5MHz, G4.

I am considering this because I am working with Final Cut Pro 4 and Photoshop and the imac is just a bit slow for this. (I have edited a 50 minute documentary on it and it has held up fine). After this month I will no longer have access to the dual G5s at school and want something better than my imac that I can edit on fulltime. (I accept the fact that it will be a few years before I can have the G5 tower in a home studio :biohazard ).

I need the portable Powerbook but am not sure what difference I will see in basically upgrading from 800MHz to 1.5MHz. I know I can load the Powerbook with memory and probably will. I am mainly editing film and not doing graphic design. But . . .

What significant speed or power gains will I see?
Is it worth getting the 128MB Graphics Memory?
Is it worth getting the 5400 rpm harddrive?(what does this do?)
and of course the million dollar question . . .
Is it worth waiting for a G5 or dual G4 Powerbook(would the gains be that much better)?