If I was to set up a run of say 250' using RG11 cable from the dish to a HD STB, given that the sat signal was strong to begin with would the signal be reliable at the box? Would I need to use any other gear such as power boosters/RF amps (and if so what brands to look for)? Thanks for any help.

Max.....
IMHO, you SHOULD be fine with this length run of RG/11 (vs RG/6), without the use of any other amp(s)/booster(s).....
The "de facto" max length run for RG/6 (solid copper center-conductor, full-shielded) seems to be about 150' (according to my installer, who's been doing this type work for more than 50 years....!).....So using RG/11 @ 250' SHOULD work OK....Good luck!

thanks