At least every Mac can be used fpr Audioproduction.
I´m a Pro and I started in 2000 with a G4 350 Mhz and this old Baby ist still runnin in the Studio (now with Protools-Extention-Cards), but even before I did a lot of good Music on a High Level on that Granny-Mac....you only have to deal with the ressources .
Here at Home I done my Stuff for the last 2 Years on a Powerbook G4 1,33 Ghz and I pushed that one allways straight to the Limit ( coz nowadays the Plugs and Softsynths are no longer that ressourcefriendly as in the Beginning..)
So 2 Weeks ago I got myself a IMac (white) 17" with Intel Core Duo 1,83 Ghz and this is a performance Blast for me....before I need to use the Freeze-Function or I bounced complete Tracks coz of the Performance Limit, now I don´t...
But in the End, the Mac & the Performance of it only define the Way you Work, not the Quality of the Outcome....