Thanks so much for the replies, they’re much appreciated. I edit in NTSC Anamorphic 720 x 480 (DV) format. I know that the CPU controls the speed of exports and renders, but was told at the Apple Store here in the UK that adding more RAM would make things far faster when it came to renders and exports.
I use a Lacie 1TB external drive just for my edits.
Best,
Russ