sv only in the mind of a fool could the questions not have been answered. As I said and continue to say.
1) There is a perfomrance gain to be had from performance top end bearings, it's the reason a lot of race teams run them Stendec who do the race tuning for the Intense race team and also Giant and Specialized's race mechanic. All who I have spoken to at length during my research and who have confirmed the fact. If you wish confirmation call them yourself and simply ask. It is also the reason that good quality performance bearings are used by the car industry as the maintenance time offsets any benefit from saving money using cheapo rubbish.
2) It is possible to improve the performance on MTB frames over and above the standard factory spec, That having a rear end action that is stiff but smooth in it's action without any flex is a good thing. Just like running a through axle on your wheels will eliminate flex so running performance bearings will do the same thing, The action will be stiff but smooth.
3) Caged bearings have a good portion of the bearings surface covered by the actual cage and will more likely than not have grease trapped between the cage and bearing surface. I would think just as anyone who has an IQ above that of the average donkey, that this fact will make it harder for the dirt to sit up against the bearing and sieze it, with the cage in the way of the dirt.
4) This isn't actually aimed at you to be honest as I believe that no matter what answers I give you will be man enough to admit when your wrong, or smart enough to know you are. There will be some who have the intellect to understand.
northwind you start to wonder if someone who sells caged bearings for part of their income has ever actually seen a caged bearing? Genius.