1) 2) & 4) are sane, reasonable and common. 3) however is not common at all, in fact I've never come across this behaviour in several years of swimming in multiple places. I just don't see how this would apply if there are not enough lanes for different paces. It does not scale at all. One very fast swimmer could easily dominate a lane, everyone would have to watch out for him/her. When you have more than 4 people on a lane, this is heavily annoying. If everyone applied 4), this wouldn't be a problem at all.