I just replaced my axles on my 08' BH. I went from the OE 6,000# Lippert axles to Dexter 7,000#. I talked to the shop that does all my axle/spring work and he looked at my OE springs and did not recommend changing at this time. He went on to say, when I asked about the heavier springs, not to go any heavier on the springs. He said that it would/could affect the ride and you don't want too heavier springs. He also said if and when I do replace the springs not to go back with Lippert. He said a lot of the springs manufactured in China are just not up to par.
Good luck on your decision.