Yeah, it's pretty difficult to judge a show based on previews. Few, if any, tourists and infrequent theatergoers (who tend to be the ones to buy higher-priced tickets) will buy tickets for a show until it's opened so they can read reviews and have more information about it. Also, shows paper a lot in previews since they are interested in generating excitement, not to mention the fact that lots of critics are watching the show as well.
In short - it's too early to judge Bonnie & Clyde's numbers. The only disturbing trend would be if it loses money from week to week in previews since shows try to build up to opening night. As long as it earns even more $ next week, it's fine for now.
Scratch and claw for every day you're worth!
Make them drag you screaming from life, keep dreaming
You'll live forever here on earth.