Generally speaking, when you get to distances required by the OP (1650 feet), you are simply extending telco services from the road to the house. Telco's cables down the street are all POTS (plain old telephone service) cables, not "Cat anything". Plus the fact that, when comparing a linear foot of PE89 direct burial POTS cable vs a similar length of Cat6 - once you untwist the twists on cat6, it will be approximately 20% longer - hence will have 20% more attenuation. If you're on the distance edge for DSL service (generally 15,000 cable feet), that extra 20% can put you over the edge. And it doesn't get you any benefit. The dirty secret in the industry is that most benefits to using cat6 come from the pens of the marketing folks. Granted, there are some instances where catX may be better than POTS - such as using an Ethernet Extender between two buildings on your property. But this is rare. Like an earlier poster suggested, in an "on campus" situation, optical fiber would be a much better solution as it is lightning-proof (ahhhh.... it just rolls off the tongue).
So, if it were "Mike and Mike's money", I'd install PE89 (black jacketed direct burial with goop) inside a 2'' PVC along with the .500 or .750 coax and a spare inner duct for another pull.