If you're really bored or really interested, take some of the speculation out of the debate with this neat little model - perfect for a sleepless night in the bunk!
Aircraft Operating Cost Calculator - Freight Metrics
Obvious limitation is that it will only produce results for US, UK and Oz, but the relative costs of the types will still give an idea of how they compare.
Having lit the fuse, I'll now retire to a safe distance.............
7B