I love switch rods, great fishing tools. I have a couple 11'9"ers (6119 tcx and 9119 method) and while they aren't noticeably shorter than my 12'6" fishing and casting wise; the shorter, thinner, lighter "switch" handles make them feel so compact and light in hand they feel like a toy. I love them and primarily use them in situations where I'm fishing 60' or less from rod tip to fly but I can definitely drop the hammer on then and shoot more line but mends get touchy at distance. I'd like to add another shorter 8wt 11'er but haven't pulled the trigger because I still haven't hit a real life situation where I've actually needed it, I think I dream up reasons to buy rods but at least I'm practical enough to see that I guess.
To the original question (I think), in general terms, the longer Switch rods will spey cast better, and the shorter Switch rods will be easier for overhead. Of course the rods design is a factor. I personally find the sweet spot around 10'6" and 11'. Does both well. "Swing both ways and have twice the fun." YMMV.