powerbook (15" or 17"?)

recently lent my 15" Ti PB (1GHz) to my brother, his house got broken into and the rest is history (painful, yet i had backed up a week before )
looking for a replacement now, confused between a 15 and a 17. i do have a isight 20" imac which has the same resolution as the 17" and its beautiful. but is it worth spending another AU$700 for a better resolution and 40GBs of extra HHD space?
am i missing something???


EDIT : also which is better 100GB @ 7200 or 120GB @ 5400. obviously 120 gb has extra space but what are the advantages of a faster drive (real-world)?

worth $400

just checked up the price of the 15 with 100GB @7200.
revised price difference is AU$400.
so all other specs are the same b/w the 15 and 17, just the screen size and resolution. i'm just not sure if its worth spending that much more. but then again, i'd love the size of the 17". ahh what to do.. ?