Never had much problem with all my 500's ,had 206's can't say much difference in running costs really other than you get a faster machine able to carry more with a 500! Big problem is their second hand values are huge, but they hold on to their value.
Would never ever have a C20R engine they are a heap of junk in a 500. All the 500's I know that have had engine problems have all had C20R's. I think it is to do with the engine being mounted at 45 degrees ?????
On another side I know which I would want to be in if you stuff it in !