Well, the most I've ever gotten was 5/Mbps in steam, so it wouldn't matter if I switched over to something that was 20/Mbps then, right?
b=bit
B=byte
I think you mean the most you've seen was 5MB/s. (uppercase B) If you're paying for 50Mb/s (lowercase b), you were getting just a bit less than your max.
So if you switched to 20Mb/s, you would lose more than half of your speed.