Higher speeds do seem to help the life of the IMS bearing. The additional oil spray can't hurt either.
Bearing life can be predicted statistically based on degree of risk. Tolerances, finishes, hardness, lubrication, etc. All have an effect on life.
While the IMS bearing is not a high speed bearing, centrifugal force on the balls will take some of the load off the inner ring, which is the more highly stressed ring. Also, as the speed increases, the balls will tend to ride up on the oil film, (think hydroplaning), limiting the metal/metal contact between the balls and ball grooves. This is called EHD. (Elastohydrodynamic lubrication)
This is a two way street. Too much EHD and the balls will stop turning and skid, resulting in wear and debris. A little slippage is OK. There are complex computer programs that will analyze these conditions.
The oil film is very thin so the peaks of the surface finish can pierce the film and make contact with the balls producing local high temps and small particles. (Think a grinding wheel) This is another reason the oil in a failed bearing is dark and smells burned
Other things to consider are stress and deflection. Ball bearings can operate at up to 350000 psi Hertz stress. The steel of the balls and ball grooves will be flexing and will eventually crack. If the stresses are low enough, and with good lubrication the bearing can last indefinitely.
The IMS bearing sees varying temps, loads, speeds, accelerations and marginal lubrication. A difficult application. There is always the cost factor.
The other end of the IMS is supported by a shell bearing and would have to be pressure lubricated by the engine oil pump.
There is very little room to put a shell bearing on the flywheel end of the IMS. I have a crankcase half and an IMS. I'll try to post some photos.
Ed B