help

Ok I need some help here. can any one tell me what the difference is between a 1986 and a 1986.5 toyota supra. I am considering buying a supra turbo from a local dealer for $2,500 but neither of us know which one it is. any advice on how I can determin if its an 86 or an 86.5 would be very helpful. I also have a couple of other options about my next car purchase. The dealer also has a 1989 mazda RX-7 and a nissan 240sx convertible thats roughly as old as the supra and the RX-7. Disregarding their current conditions which of the three would have the most potential performance wise.