I'm bringing power and phone lines from my home to a workshop on my property via buried conduit. The pull is 500 feet. I also want to pull coax cable for a TBD future use (probably satalite TV or high-speed internet). Would RG6 be sufficient or do I need something bigger like RG11 for a pull of this length?

You would require something more substantial than RG-6...
RG-11 would be a minimum for RF signal carriage for anything at this distance. For TV Antenna or Cable TV, the one RG-11 would suffice, providing that the loss was pre-emphasized (moderately amplified) to account for the loss of the cable after said amplifier (Gain=Loss). For proper amplifier gain selection, the signal levels (Highest/Lowest Frequencies)prior to feed into the cable should be known.
 
For Satellite Carriage, you would be stretching the limit at 200 to 250 feet. This would require amplication somewhere in the middle, a middle you probably wouldn't have access to. I have had customers avail themselves to hardline Coaxial Cable such as .500 (half inch 75 ohm commscope) or .625. This is the stuff Cable TV companies use as their distribution line (feeder). This cable usually comes on 2200 foot reels, and as a whole reel, can be pricely. Partial reels however, are cheap and easy to come by via your local cable TV contractor or military auction (who will probably have several partial reels laying around). Connectors for this cable are around $5 a piece (we supply to cable companies as well). One customer had a RG-11 run of 400 feet plus inside wiring, with a no go signal. Completing the .500 install himself (after a crash course given by yours truly), he enjoyed a 99% Signal Level reading across the board. Otherwise, you'd probably be better off simply investing in another Dish (line-of-sight permitting).
For Internet, if it is via the RG cable or Telco line BEFORE the Modems, you're good. If you're talking about running a CAT5e or CAT6 connection AFTER the modem, you need to re-think your install as the limit is typically around 350 feet total.
Finally, the last thing you want to do is run communications lines of any kind in parallel and in close proximity to power lines. This is a no-no, shielded or not.
The Soil itself is a great inhibitor of man-made transient electro-magnetic fields and flux, this will help you in rejecting ingress and interference. But in addition to this, simply give yourself a couple of feet minimum between the two.
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Good Question
Thanx
ed