On good advice from a buddy of mine (after a really rough losing streak in steelhead early season), I ran circles the rest of the year.
My results were as followed:
Trout bead: You almost (literally) never miss a fish. Landing rate went from 40-50% to the high 90's. I fished a sliding bead above a size 4 (regardless of bead size) gammy circle for the absolute best results.
4 inch worms: I did not lose a single hooked up steelhead. Fish typically hook themselves. I will not fish another hook with a 4 inch worm ever again. Size 1 circle gammy was best.
6 inch worm: Didn't work whatsoever. The fish seem to bite the middle of the worm and never really get hit by the hook. I wouldn't ever recommend a circle with a worm larger than 4 inches long.
Bait: Very mixed results. I lost 3/4 steelhead with size 4 hooks during steelhead season on solid float downs/hookups, so abandoned it (especially after the spectacular results on other methods). I have been trying them again Chinook fishing on the stamp. My findings is that you need a minimum of a size 1, but a size 1\0 is better (so low clear conditions on spooky fish it won't be ideal). Roe needs to be smaller than the gap of the hook so as not to cover the point. You do miss some fish, but we haven't lost one yet that's actually been hooked.
Roe bags: hang the bag off the bottom of the bend of the circle hook. We used size 4 gammy hooks again and so far the method has been 100% on hookups (granted small sample size of 5 fish - I dislike roe bags in general). I believe this works well because the hook point never is covered. Prawns have also been 100% landing rate with well over 20 fish hooked now - same thing, thread it on and hang it off the bend of the hook.
Spoons: took a lot of tweaking, but I'm fairly confident in them now. Overall I'd say on steelhead that it is similar to normal hooks on a trailing system. Maybe slightly higher. Size 1 hook is the sweet spot. Where they shone was on brown trout for some reason, landing % was up drastically. I look forward to trying on coho.
Other notes:
I was told when starting to not set the hook with circle hooks. I've personally found that to be false. I tend to reel down quickly until I feel some weight, and then set hard every time, and it has worked very, very well.