Get the lowest rings possible that will still clear the objective bell without contacting the barrel. The only caveat to that is to make sure and take a spent shell casing with you to ensure that the windage turret will not interfere with ejection when you mount the scope.
A 50mm objective should be able to clear in a set of medium rings and bases in most cases, unless the actual objective bell diameter is really really over sized for say an adjustable objective. As low a mounting as possible is desirable in order to keep recoil strain on mounts and optics to a minimum, additionally the lower mounting promotes a better and more consistent cheek weld on the stock which will usually result in better more consistent shooting.
The advice to get see through rings is perhaps the worst I have ever heard, all those manage to do is set your scope so high up that you can't get a good cheek weld. Additionally the extra height typically makes for a much weaker mounting since the leverage between rifle rings/bases and scope is longer and easier to torque under recoil. Another downside is the fact most are made out of the cheapest aluminum available and they are weak to begin with to mount a normal sized scope in, much less a large objective high magnification unit that is going to have some weight to it.