How noticable is the speed difference between the 1.2GHz and 1.33GHz 12" iBooks? Is this a good deal for $675? 1.2 GHz G4, 512 MB SDRAM, 60 GB HD, 32 MB VRAM, Combo Drive, Airport, Bluetooth. I could upgrade the RAM which would speed it up... but should I just go with the newest rev. (1.33GHz)?