Consider a MacBook Pro with a SSD
I've had a PPC G4 17" from Jan2005 thru Jun2011 as my main machine. Although I still have it, I've given that role to a 17" MacBook Pro, w/ 8GB RAM. It screams.
Do consider a Solid State Disk; mine is 120GB only, as I didn't want to buy truckloads of TB's of external storage for backup and cloning, etc. The point is, SSD's are much faster and more reliable than traditional drives, although I clone and backup daily.