I am doing an Olympic distance in late Georgia April. Water temps a week before the race are 67 F. Really do not want to get a wetsuit if I don't have too Rent or buy). I can vasoline up my lower legs, arms, neck exposed from trisuit. What temp is too cold? I'm pretty sure 67 won't kill me for the half-ish hour it takes to finish the 1.5k, but will is zap so much heat/energy that I may as well ride a tricycle?