Even though Page RPM can get quite high, I can't say that I notice a massive difference in earnings. The amount of earnings I get normally correspond to the clicks and CPC.
I am not sure what you mean exactly. Earnings, RPM, CPC and Clicks are all related.
CPC = Earnings / Clicks
Earnings = Clicks x CPC
RPM = 1000 x Earnings / Page View
RPM = 1000 x Clicks x CPC / Page View
Which is not accurate, since you also have CPM included in the Earnings, but Adsense is just doing the math Earnings / Clicks to obtain the CPC, so it's only indicative value. Also, if you do the math, you'll find it's not always exactly matching, it might be a matter of rounding some intermediate numbers, or some data being delayed.