I have a MBP. it's 2010, 15" with an i7 (2.66ghz), 8GB ram (ddr3) and a Descrete Video card. (geforce 330m 512mb)
It runs
Qlab just fine both video and static jpg images. It is worth nothing as mentioned above that doing effects sucks up more resources and it can stutter a little
bit.
You're a veteran here so I don't want to preach to you.
Figuer53 has some articles about the best way to encode and render files for maximium effeciency that are great and well worth taking a look at. I don't normaly run super efficient video/images and this 5 year old MBP still runs stuff fine.
You will be solid on even a
base 1100$ model for a modern MBP.
That said what everone else said here I'll reiterate. 16mb RAM upgrade (is a cheap life extending upgrade right off the bat, that can get more expensive down the
road being
Mac/Apple closed
system) You'll find the computer more responsive with a "descrete" 3rd party video card rather then the Intel Integrated HD chips. Then
throw in the fastest CPU you can with your budget. I'd even say you could keep your internal HD fairly small, though SSD is still a must. (running your media from a firewire drive works just fine as far as bandwidth goes for anything that i've encountered.
http://www.apple.com/shop/buy-mac/macbook-pro?product=MF841LL/A&step=config#
It looks like you can't ge the descrete video cards (no Radeon apparently) in the small/cheaper MBP configuerations....typical. If you have the extra 200$ up the
processor, if you got an extra 800$ step up to the MBP 15" with descrete video. (2800$) That said I do believe teh 1099
base 13" MBP would suite your needs just fine based on what you said you'd use it for. But Future proofing as you know is always something to consider as well. As my MBP can attest, my near top of the
line 2010 model is trucking along nicely still.
[EDIT]
I presume you need the portabitliy of a Laptop. If not in comparison to the high end MBP the
base Mac Pro (trash can tower) gives you a HUGE
power jump for
base price of 3000$ One that you can edit video and do anything else on to your hearts desire.
I also wouldn't neglect the various insundries needed with any
mac purchase (tower or laptop) things like Video adapters (the extra long
power cable for the laptop brick) protective case? USB
hub, (newer ones only have 2 USB I believe), optical drive, thunderbold to firewire 800/400 dapter (for things like audio interfaces/cameras),
etc