Having used both single and twin discs, and P34 calipers (single and twin) and now using twin stock calipers...
I'd reccomend using twin discs with standard calipers and the pad of your choice.
That's also the conclusion that Geoff came to when I spoke with him last year.
I think it's the best compromise on power and feel.
I'd use that on a 583 too - purely coz I've had trouble with single disc set-ups in the past - mainly when I'm trying to stop from 100mph and they stopped stopping!!!