I have a Newport 27 TM (kinda since I am in the process of selling it). One of the prior owners put together a polar chart for it. Let me know what your email address is and I will be glad to scan it for you. I am not sure how accurate it is, but I often use it as a rough reference.
As far as the reefing goes, if you are going to carry the 140, you probably want to put the first reef in about 14-18 knots of apparent wind. It depends on how much heeling you are going to tolerate and the weight of the crew on the rail (if any). However, with our boats it is typically better to switch to a smaller headsail rather than reefing. You can easily sail with a 100-120 headsail and full main in the low 20s apparent.