I'm getting a comfortable controlled life of 40- 50 hrs for RPM Blast 18 strung at various combinations in the mid 40# range in a Head Microgel Prestige Pro, after which it gets a bit boardy and vague, and I cut it out. What seems weird to me is that this occurs when the mains are about 30-40 % sawed through, which is when my former favorite Wilson Sensation 17 played its best.
I find RPM B to be amazingly consistent throughout its life. Much better than Sensation 17 at 52.
My observation is that that the problems with RPM B arise when it is strung at tensions over 48#. I do not like it at all over 51 or 52--I would not use it if I required tension over 48.