Re: Ring spacing
Assuming the base to which the ring is attached, rail or otherwise, can adequately perform its role, place the rings as far apart as possible while maintaining proper eye relief. This will ensure that the cantilevered length of the scope is as short as possible. In the event that the scope is struck by something, like the ground if the rifle is dropped, it will likely be that fat parts of the scope that will take the hit, and as these are often cantilevered from the rings, the shorter cantilever will be more durable.
This also illustrates why large diameter scope tubes are nice, like 34 and 35mm. They are simply much stronger than the smaller diameters when subjected to bending loads that could be encountered when the rifle is dropped and the scope's objective bell takes the hit.