That certainly depends on how the law is written. Where I live, the wording is that you are recommended (and on certain roads, required) to stick to the rightmo

That certainly depends on how the law is written. Where I live, the wording is that you are recommended (and on certain roads, required) to stick to the rightmost available lane – which means that you're certainly not breaking the law by driving at the speed limit on the leftmost lane if all the other lanes are already at full capacity, which also makes perfect sense to me. (However, exceeding the speed limit would be against the law in any situation, unless perhaps where you could avoid an accident by doing so – although that may be hard to prove.)