I’d get a used one. Bout 2-3 years old should be fine. It’s the time the battery starts to deteriorate usually. But since us DJ folks don’t DO battery-operated, that is hardly an issue.
I would tear out the HD and put in an SSD though (Samsung 840 Pro is best atm imho). Or take out the CD/DVD-player and get the tray to add an SSD (depending on the amount of storage you think you really need. I think that if you DJ and you need a couple of hundred GB for your music you might have too big of a collection, but that is just me 😀 .
Upgrading to an SSD is the single-best performance enhancement you can make, especially to a slightly older machine.
Any dual-/quadcore processor should work fine if you don’t plan on doing some very heavy audio/video editing or a zillion stacked FX. Personally I think i7 is a bit of overkill (but nice to have for those that have a fitting budget :=P ).
4GB is ok. 8GB is very nice to have.
Just my 2cents (which unfortunately is way too little for an MBP)
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