My majesty clip file generally needs 200 for one cloud layer, and most of my top-quality scenes total around 300 to 400 cloud samples for all the layers combined (on average 3 to 4 layers, but if i'm trying something special - like my IOTW71 render "paradise", I'm using 5, maybe 6 cloud layers).
Seriously, I generally don't notice that much of a drop by increasing cloud samples since I render overnight, so I set cloud detail to 1 anyway, because I'd rather have it take 1 hour of my time longer (which I will be sleeping through anyway) than for me to have to render again and have wasted a night.
Even when I'm rendering in the day my most complex scenes (apart from ones with extra lightsources or reflections) take less than 2 hours each, which I'll happily do on my laptop while I'm doing other things with my PC, like making more tgds.