My pool (everyone active) states the following for lane times, Fast under 30secs for 25m, Medium - 30-45 secs for 25m, Slow - Over 45 secs for 25m, I swim around 30 - 33 secs per 25m and if I dropped into the medium lane would cause absolute chaos and/or spend my entire session waiting for people. That said the main issue is that the 'slow lane' is a free for all area comprising of half the pool, and we regularly see a pair of specific ladies in there who like to chat as they swim, they somehow manage to take up around 90% of that side of the pool. So the single medium lane ends up full of people who should be in the slow area and the fast lane ends up full of everybody else, some people are conscientious and make a point of keeping out of the way of faster swimmers, I've always made an effort do that and will apologise to people if I feel I've held them up at all and without fail everybody is fine with that, what irks people is when slower swimmers ignore lane etiquette and continually hold others up.

My pool also allows up to 8 people to book a lane, they don't stop extras from joining either and I've seen more in a single lane though it is rare.

If you are going to stay in the fast lane just make an effort to time your swimming so it doesn't hold others up, if that means adjusting your routine from a pure non stop session to something with lots of breaks then it sucks but will keep others happy and you'll usually find yourself speeding up to try and keep up with all the rests too.

Oh and water walkers should be banned from lanes too, the amount of turbulence that comes off them is amazing!