Don't worry about it, Roadie. On race day everything is different, including the boredom level (or lack thereof). On a good day, you can kind of feel swept along - you can actually find yourself in a drafting situation, to a certain extent. Of course, I haven't done one in 2 years, so what so I know. Anyway, just go for it, and an your race will go by much quicker than an ows by yourself. As far as getting tireder in open water goes, well, you can't do flip turns, and it can get fairly wavey, which is tiring. It's normal.

By the way - be VERY careful out there swimming alone. I've been swimming all my life, but I don't think I'd go alone, except at a pool, especially with jet skis & speed boats around. It sounds like you are making all the correct assumptions, though. Okay, so not all jet skiers are drunk (I have to keep telling myself that, since I have a friend/former co-worker who is heavily into that - I try to be open-minded, but it just doesn't come naturally), but better to assume the worst, if it keeps you safer. I just did an ows tonight, with my DH and my friend - even with 3 of us, we're continually checking on each other - machines aren't the only hazards out there.