I don't think a pot can be too big, within reason of course. If your trying to do 5 gal in a 300 gal pot you won't have good luck. The wider the opening the more evaporation you will have, so you just need to take that into consideration.
I think you'll love having a 60 qt pot for 5 gal since you will greatly minimize the risk of a boilover.
Agreed, I use a 15.5 gal keg for 5 gal batches. It takes nothing to cut the top off of one. And with all grain, scorching isn't a problem as all of the sugars are mixed in with the water, no syrup or sticky powder to deal with.