the problem with using one climb as a "benchmark rating" is that it leads to grade inflation.
If climb X is "benchmark 10a", sooner or later Joe Crank will put up a new climb, Climb Z, and say that Climb Z is 10b because it is harder than Climb X. Then the existing Climb Y, that was 10b, will be upgraded to 10c because it is harder than Climb Z and so on.
What you really need to know is the easiest and hardest climb at a particular grade. For instance if you know that Orifice Fish is the hardest 5.9 at Squamish and that Arrowroute is the easiest 10b, then you can say that Exasperator p1, being easier than Arrowroute and harder than Orifice Fish, is 10a. Except that O.F. is probably harder than Exasperator p1 and personally I think Arrowroute is easier than Exasperator too.