Personally I wouldn't take the chance going that early. As you said it can be hit and miss depending on spring weather and water temps and chances are they will be in transition moving from spawning areas to their summer haunts. Plus you will be dealing with changing weather patterns that can make for a lousy vacation. For example here in the Ottawa area we've had frost in late May for the last three years in a row. If it was me I'd pick the full moon in the first week of July, weather should be far better and the bugs will have subsided enough to make the trip more enjoyable.
Cheers