Macbook Pro for music production

I'm looking to buy a Macbook Pro for music production, budget being $1700. The issue I'm facing is that I've been scouring the net for ideal configurations, but am stuck between the 13" 2.8 Ghz MBP and the 15" 2.2 Ghz quad core MBP. Also, these rumors of a possible March launch for a new MBP have done my head in.
I intend to run Ableton, FL Studio, Reason and Massive Synth on the laptop. Size isn't a problem for me as I don't mind lugging a 15" around for gigs.

Would appreciate any advice you guys have for me.

Thanks