Wetsuit or not?

At that temp especially for a short event... I would not wear a wetsuite.

The difference in speed of transition would more than make up for any swim advantage the wetty would give

I wouldn't wear it.  The water is plenty warm and IMO for a race that short the time you'd possibly gain by wearing the wetsuit would be negated by the removal of the wetsuit.  Whatever your decision, good luck!

I am about 7-8 sec/100yds faster in a wet suit too. for 300 yards I might save 20 seconds. If I can get out of the wet suit in less than 20 seconds then I would be faster to use it, but in a short race the fewer things that you have to do in transition the better.  You don't want to increase your chances for error.  At one race I forgot to take off the timing band before pulling the wet suit off it got stuck and the ankle and I had to put it back on remove the timing band then doing things over again which added about 30 seconds to things.  Another race I put some equipment the timing band in my teeth to keep it out of the way during the peel and the timing piece slid off the velcro strap.  I didn't notice it slid off.  One of the peels scooped it up off the mat for me and brought it o my bike but threading it back on the velco strap took some time.  It was like threading a needle.  So..minimize you equipment and if an its potential for saving doesn't exceed its potential for losses.  In a 2000 yd swim if you are 7-8 sec/100 yds faster then you might save 2-1/2 minutes. Even if you loose 30 seconds you still come out ahead.  If you are only saving 20 seconds on a shorter race and you run into trouble and loose 30 seconds then you were better off with out it.   

Here's another spin on the answer, which may make all the difference.

Everyone always looks at the balance of swim speed vs transition, and leaves off the rest of the race. For me, even if it's slightly slower by a few seconds to wear the wetsuit in the swim and take it off in transition, my legs are warmer going into the bike leg, my body overall is kept warmer and better balanced, and I'm faster on the bike immediately. I've worn my wetsuit in many races where the swim was as short as 300-400m.

How fast are you getting the wetsuit off?  I watched guys for years show up in transition with their wetsuit down to their waist......and they were stepping out of it while they put their helmet on....no time lost.  Most people don't have a clue how to trim their suit to make it simple to take off.....or they just don't want to cut it.  It's not a big deal, but whatever..

Overall.....everybody in this threat is right....because you have to decide what is beneficial and what is not for YOU.  The rest of it is just noise.