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Here is the conclusion: Send a lot of short messages. Even though a short message may not give you a high probability of scoring for any one potential match, you get a better overall return on investment. That is, you can send more short messages to a lot of people. In the end you will get more responses.
The real killer from this post was the phrases in your message that would give you a better chance at getting a reply. The best phrases to use are awesome, sorry, haha, and pretty. The worst phrases to use are ur, im, hit, wanna, and beautiful. Go figure. Pretty is better than beautiful.