I have an ancient Mac (Quicksilver733) running Cubase VST5, a MOTU 2408mk2 audio interface. a Midex3 MIDI interface (do NOT get one of these for OSX!), a couple of UAD-1 cards and Mackie HR824mk1 monitors.

Despite it's age, it has successfully run over 36 track projects and VSTi's (I freeze as fast as possible!). Primarily, I do MIDI production and some light audio projects, so it does OK... It's close to bomb poof, and that counts a lot more than the latest gizmos, in my book...

Main keyboards are the G70, a K2500S fully loaded, and a Triton.

Basically, if you can't make a decent track with this, better gear won't help!