Re: Switch rods..
The grain window will be dependent on the caster and the rod. For trout and summer Steelhead fishing that I do with my 11 foot 6 weight, 325 to 375 grains shorter Skagits should do the trick. I recently put a 375 grain head on my rig, and it makes throwing size 4 rubberlegs stonefly nymphs rather easy.
If I was going to dedicate a switch rod for Steelhead fishing, I would bump myself to a 7 weight rig. The grain weight range would be higher. I'd need the mass to throw some of those large Intruderish flies.