There are great units for purchase. I realize you know what you will do with it, and your needs.
If you want to use it for music, I have a laptop 6 years old, and it will run Sonar X3 easily, Splat too. I have learned patience though, let the laptop do it's work, don't rush it, just like you wouldn't a good person who might take time to complete tasks but completes them in fine fashion. It handles video render and AE CS 6 too, just be patient.
Of course, if you have the jack, get the top o the line. I don't believe you would regret it in the long run, which I know you are in for, the long run that is.
Jesse Q. Screed
Jesse Q. Screed