Wetsuit question.

I know that this is an oft-debated topic, but I'm rethinking registering in the wetsuit division of the RCP Tiburon Mile in September. I've only recently returned to swimming after two years of doing only cycling. I have about 10 weeks to train for the swim. But... I tend to run warm. On the bike I often seem to be wearing far less than most riders on cold days. And the attached picture is me, swimming in the North Sea in 2005. All I was wearing was a thermal cap and and ordinary jammers. I stayed in the water for about 15 minutes. I only got out because my wife was waiting on the shore and getting impatient, and I thought I saw a jellyfish. I'm not so much worried about the cold so much as not having the stamina to make the crossing without a wetsuit. I know that a wetsuit will allow me to stop if I need to. But is that a legitimate concern? I can swim a mile without stopping, or at least be able to by September. The current is forcasted to be pushing us about a quarter of a knot or so. The water should be a little over 60 degrees. And I did the swim in 2004 with a wetsuit. I told myself that I'd do it next without one. Right now my distance pace seems to be around 2 minutes per 100 yards.