I think the speed limit could be increased. It's a unique idea to have a different speed limit for the left lane as compared to the rest of the lanes - but I'm open to hearing it.

Also - the left lane is the passing lane. Doesn't matter what the limit is - use the lane to pass and then get out of it. If you don't need to use the left lane to pass because you're in one of the middle lanes and no one is in front of you, then great! Leave the left lane open. In case someone else wants to pass. If you are the ONLY PERSON ON THE FREEWAY and you aren't in anyone's way - there is still no reason to be in the left lane. Because you aren't passing anyone.

It doesn't matter if you are going the speed limit or well above the speed limit - once you are done passing whoever you are passing, it's time to get out of the left lane. If the left lane is wide open in front of you and someone is behind you and would clearly like to be going at a speed faster than you, but you are also passing people to your right, it may make sense to move over long enough for them to pass you and then you can get back to passing the people you are passing. I say "might" because there could be multiple variables at play and there may be times it does not make sense to do that. But most of the time it does.