The K85, as mentioned above will be plenty off grass. As to my runway, FYI, i have 800' paved and the same grass right next to it. My dry weight came out to 25lbs and TO is with a gallon of fuel and if my A&P memory recalls, i think we used 6.6lbs per gallon for specific weight of JetA.
I believe the Turb2 with the 85 will be an overpowered setup and that could lead to issues in landing speeds being higher than needed and as your first jet, that will get you into trouble. If your getting the KT85 then i would suggest opt for the larger Turb V2 and if an 81" plane is to big, save some money and go with the Turb2 ARF and use a 60 size motor. I feel you will not be disappointed on either setup.