I was told that the quality of wireless connection follows the law of the lowest common denominator - meaning that if 10 users connect to an AP at 150Mbit and one at 54Mbit, everyone gets stuck with 54?
Thank goodness, no... :) so smart of you to second guess this. In fact the AP/Client makes the data rate decision on every packet. This means that when your client says 150, it probably means "mostly 150".
There is one thing to understand though, if one client is at 54 and another is at 150, the client at 150 consumes 1/3rd of the "airtime" of the 54 client to send the same data. If slow clients send a lot of data they can significantly slow down fast clients. Our feature Dynamic Airtime Scheduling can prevent this - I would recommend reading the Dynamic Airtime Scheduling Whitepaper as it goes through this in detail.