Thank you for both responses - Triplets - I sort of agree - could be the case, is processor speed the issue though as many newer Macs have less RAM? And Fuzzfilth - thank you for those additional tips = some of which I haven't tried and will do so. Freezing tracks always feels a bit premature when working on something that isn't finished but it's possible - and yes Alchemy is there of course.
But processor speed the main issue here?