Don't go mac, I bought an Vaio with equivalent specs to a macbook for 3/4 of the price, spent the difference on 8 additional Gb of RAM and a 500gb SSD.
I think if you already have a decent laptop get a desktop - which is what I should have done since I have a triple monitor setup and two usb hubs all plugged into my little laptop.
I have mixed and mastered professional albums with it and at max hit 70% cpu usage (i7). I'd like the power of a desktop so I can be a bit more reckless with my plugin choices, but then again, tracks that I've made off it while lying in a hammock at the cottage have been placed and whats more convenient than that?