Made mine a 2 pc, so the top half folds outward and lays on the hood. Had that on an open trailer with no issues at 70 mph, however it was folded down! Mine also has an aluminum angle going all the way across to support the windshield from flexing. Mine is also made from lexan, it wont break...mine is held on with 4 strap clamp mounts, can be removed in about 10-15 min. If windshield is solid, what is the material? Plexiglass will break or shatter but lexan wont break at all. Might fold if thin enough.
65-70 mph is a much greater wind force than 40 mph by far. You dont have a roof so that will help. Next is how is your windshield mounted? That might be a more critical issue. Hate to see it buckle and come off. Also depends how your towing your 450i...forward or backward?? If you go with bracing be sure you are supporting the windshield on the correct side. Dont put your braces where you look thru, or the windshield may scratch from having the wind vibrate against the brace. Just throwing some things out there to think about before you head out. You might consider sawing your windshield in half and add a long piano hinge to allow the top half to fold down, that would cut your wind resistance in half. Let us know what you decide....safe travels!!
