Great Planes Super Sportster 40, or Sig 4-star 40 are both doable builds and will keep you entertained in the air. I built a SS40, powered it with an OS 46 AX and it's quite fast and aerobatic. My 4-star is a 60 size but I'am sure a 40 size with your OS 46 AX will be a great combo. Of the two, the 4-star will be the more gentle to fly and land (better on the rough grass field), and the SS 40 will be more of a "hot rod" and would need a modified landing gear on your rough grass field. The Goldberg Tiger 40 would be another EZ build that's good on grass. Good luck with whatever you choose.