all higehr versions dont take anything away from its predecessors,
myself i use 1.5.7, cuz it lacks a few bugs ive noticed in the 1.6.x series,
if you like 1.6.3, youll like 1.6.6 just as much (or whatever the newest version is), it will have all the same buttons , and should use the same reg code, unless of course the reason you need 1.6.3 is cuz thats what you have a crack for