6:1 is the highest you want to try and deal with, otherwise, everyone ends up sitting around doing very little climbing. A good guide can easily handle 6 clients if he knows what he's doing. We routinely run classes that size.
It also depends on what type of climbing the client(s) are requesting. If it is multi pitch, forget it with a single guide. I won't take more than two.
In some cases you either end up with a client that can belay, or you can train a person or two. You have to have your area picked out that has the routes close together so the guide can monitor both stations easily. Of course you will have to have a backup belayer.
For people who are not hooked on climbing, not having a 1:1 ratio is not a problem, and may even be preferable, as it makes the day more fun as the clients can chat while the guide is up setting anchors or free-soloing the route while they belay.
My first outside climbing was with a big AMC group, doing a "Beginner's Climbing" weekend.I was the client with the most experience, from the gym(and yes, the guides razzed me - The young one saw my shiny (BD Iris)harness and (Boreal Ballet Gold)shoes and said "Ohhh, I don't know....You better show that gear to(other, older guide). Grrr.....
Anyway - maybe the 6:1 would works, but we had 2 guides, and probably 10 people. There was some standing around, but we were all good and tired by the second day's end. Our guides had a spot picked out (Deleware Water Gap)but there was a group on weekend warriors there when we arrived. We went to a secondary choice, and I recall the guides having a little concern they wouldn't have as many routes as they would have preferred. We ended up having to take two and three runs on the two routes in the section, instead of moving onto new ones after the first run.
I guess I would say that with clients that are just trying it, and may or may not enjoy themselves when the rubber starts to slip, a low ratio is 3:1. If clients had been climbing, knew they liked it, but didn't know how to do gear, I think 2:1 would be low.
If you had a group of 6, with several of the people already having decent seconding/belaying skills, a guide with three ropes to set up could keep everyone climbing/belaying the entire day through. I don't see anything wrong with that. But 1 guide, 6 clients who have never climbed before - I think it would be risky for a guide to have them paired off and climbing in three sets all together, with them supervising.
Personally, I actually prefer climbing in parties of three even with friends, unless it is someone I know well and enjoy being around. I'm actually not the best in 1:1 situations and like the dynamic of three.