Having been .22 addicted since my teen years and having owned many of both of these guns, I'll give you my opinion.
There is no Single Six I've ever come across that can shoot with a 17/617, not on any day of the week, ever. That's not opinion, that's from shooting plenty of both. I think the potential is there for the single six, but Ruger doesn't seem to be interested in extracting it. 17's on the other hand, will shoot much better than the nut behind the trigger in almost every case. When I was in my '20's I could clearly see bullet holes at 25 yards, and with a vintage 17, I chould hit them regularly.
My first handgun was a Single Six and I loved that gun and it shot pretty darn well for a SS, but I could not depend on it to hit tiny things at 25 or 50 yards like I could with my brother's 17.
The Ruger compromise bore size is more than likely the culprit to top accuracy, and for it's intended use, it's probably not a big deal on the Ruger. The Ruger is more of a hunting gun, the 17's are more target oriented. I can remember the day that a K22, K32 and K38 ruled the matches as the top target guns. To this day, it irks me that now that I could afford all three of them, and mind you a good K32 would run you a cool $3-4K, I can't see well enough to take advantage of their sights, so they're wasted on me.
I love Rugers and the Single Six is a cool, fun and durable gun, with enough accuracy for 90% of the shooters out there, but a good S&W 17/617 is the top .22 revolver in my mind, without any competition. I've read where Colt's old Diamondback was a good gun, but never had the chance to shoot one, and with the S&W's being less than half the cost and all the accuracy, I never much cared. The only other revolver in the class is the old Colt Officer's Model Match, and it's a dandy, well able to keep up with a 17, and at about the same cost. I still see them from time to time, but again, I can't see open sights, so they aren't in my future. I've had a couple of them in the past though, and they're really good guns. I like the S&W trigger slightly better, but the Colt's will shoot.
If you haven't guessed by now, I literally grew up with a 17 in my hand, one that belonged to my brother, and I shot it far more than he did, and that includes when I was old enough to have him buy me a SS. I would still use his gun when he wasn't shooting it.