Hi Nick, as an owner of a Ti667 and previous owner of a Pismo 500 here's my bit.
For your money I'd look at a Pismo, max out the RAM and look at the G4 board for it.
The iBook is fine but I play with my wife's "little" 12" 700 now and then and for what I do it would drive me nuts.
I use many of those same programs for video and web stuff too.
As for the Ti not being as rugged, hey I work everywhere, I drag this beast around all over and so far so good.
The Pismo is a great machine, but I wouldn't keep thinking it's indestructible though.
2.6 i7 MM, 27iMac i5
1.4 MBA 11"