hey DJ Doin’Bad,
Traktor is not very demanding, but for production when using a lot of tracks with plugins and automation, you may need something more powerful than what Traktor requires.
Multicore processors make redundant tasks go faster — like analyzing multiple songs at once or paralle processing of multiple tracks/plugins. Also, the bigger the level 3 cache the lower the latency.
funny thing about the Mac is it hasn’t really improved very much since 2012, although the NEA processors coming out for Intel will change that. in the mean time, Apple has made it harder to upgrade RAM and batteries and have made a few other manufacturing decisions that make upgrading and self repair much more difficult. Retina displays have also arguably added more load to a system with little benefit — especially for music applications.
All this to say, I’m really happy with my MBP 15″ QuadCore i7 non-Retina with 6MB of level 3 cache that I bought last year for $1000. the SSD makes it scream and it can handle a lot of tracks with many demanding plugins in Logic.
If you need more info for comparing models see EveryMac.com. for buying used, it is an indispensable resource.
since music production is so much more demanding, I suggest you check out production web sites and see what they recommend.
see the LUG logic-users-group.com or he user’s forum of whatever production software you plan to use.