Just wondering why speed is a big issue for you???
Are the times very very slow?? Do you think maybe you need to look elsewhere
to reduce the process time?
Processing arrays is usually pretty fast because they're in memeory.
Maybe changing the order of processing could speed things up.
What do you call "very long" and how many dimensions?
You can switch automatic calculate off and then switch it back on when
you're done.

Sorry if it seems I don't understand clearly.

Personally... I've always found Clarity for Maintenance a much bigger factor
than speed.