For varmit hunting past 500 yards, I would indeed have a 50mm scope. Deer hunting up to 300yards, get a 40mm. Thats what works for me.

Is it worth it for a 50mm? Well you got to consider a 50mm lense is 36% larger than a 40mm. It has much less yeild after a grind, and 36% more grinding. Also do to its size, the objective bell, is tougher to make and machine to be perfectly round.