I see most guys here are fairly experienced (at least according to their profile) but flying search and rescue for a living for the last 13 years, I have seen my share of single diver deaths. I am not a huge fan of large groups but there is usually a middle ground that can be reached. I dive here in Hawaii where vis is usually 80-100 ft. and we can keep good spacing. When the water is churned up and vis low we tighten up. I have found that as long as we brief how things are going to play out in the event of low vis that cuts down on the problems.