Another thing that needs to be considered about metals, especially aluminum is the welding.

6061 is often welded with either 4043 or 5356 welding wire.

4043 isn't considered particularly heat treatable, and relies on dilution to achieve heat treating response.

4643 is supposed to be heat treatable.

I think there are supposed to be other heat treatable welding wire alloys.

Unfortunately, it may be difficult to find very fine process details on big factory made frames from China.

6061 is also supposed to be good for salt corrosion. Other alloys may be less salt resistant. Important for some riders, not for others.