I can't say because I have not sailed a N-27 but I would start by sailing the main reefed and then reef down the genoa if it gets a little too much. A 140% is a big headsail and if you are in any wind above ~20kts or so I would venture to say that you would experience some excessive heel; possibly turtle if not careful. You mention sailing on mountain lakes so you also need to be careful of downdrafts coming off the steep slopes which could cause knockdown if you are not prepared.
Start with a reefed main and depending on the wind a reefed jib. Get the boat sailing on her lines (10-20 deg heel) and get a good feel for sailing a monohull. Don't push the upwind performance and amount of heel until you get comfortable with your skills and the sailing characteristics of the boat. If you get into too much wind; spill the sails and drop to a reach until you can get your headsail reefed more and try to head up again. If the wind gets too high sail downwind so you can sail with better control (good idea to start the day going upwind so you don't have to beat into the wind on the way back to the marina).