powerbook with protools

I am considering buying a powerbook for use with pro tools for portable recording capability. I am wondering whether there is much of a benefit to buy a 15' powerbook with upgraded memory, 512 to 1 gig, and upgrade hard drive with a 4200 rpm and 5400 rpm. Any inight would. be appreciated.

definately get the ram, the more the better
the hard drive upgrade is also a good choice as you will certainly notice a difference if you're doing any heavy audio/video work, but it's not absolutely necessary