I just recently talked to a guy here at my gym who has won every comp he's competed in so far (I think 2 or 3). I mean won the overall, not just his weight class.
The most recent comp, he came in at 187. That's 11 pounds from the top of the light heavies but he won not only the light heavy but also the overall.
His advice: DO NOT target a weight class. He said just diet down and work on your proportions. Work on coming in as tight and as cut as possible and get your proportions as perfect as you can for you structure. The idea is to make your goal the overall, not your weight class. He said too many guys come in looking to win their weight class and they end up either soft because they were afraid to go too light, or flat because they didn't want to be at the bottom of the next weight class up.
His offseason is kinda old school though. He was 250 before he dieted down for that most recent comp, and he said he is going up to 270 before dieting down for his next one.
Interesting enough, Eryk Bui said exactly the same thing. 2 years ago, he won the lightweight class and he was only a few pounds from being a Bantam. Last year he won the middlewieght and was only 1 or 2 points behind Chris Cook for the overall. He said for competitions, aim for the overall, not your weightclass; come in at whatever weightclass your pre-contest prep lands you at.