call me crazy but an older i7 with a good amount of RAM (8-16gb) should be plenty for most project studios. Only reason you would need more is if you are doing something like >24 tracks and/or lots of VIs or samplers. I would try keeping your current setup with a new sequencer like Cubase. If you like it but your computer is still lagging, then you can take Cubase over to your new Mac. If you made the jump to Mac strictly to use logic i would understand, but if you have no preference in software I don't really see the point until your PC gets to the point where it can't handle what it needs to.