I noticed that there're some differences between these versions(GG and SMS). if you play the levels you'll notice that they have different design. In Green Hill Zone Act 1 you can finish it faster on SMS, same for Green Hill 2. On Bridge 2 you're only able to finish on SMS with 1:59/2:00, the GG version is faster.
So, i think that should have different rankings, for GG version and SMS version. Don't know about Sonic 2 and chaos yet, i'm going to try it later.
What do you guys think about?