I don't ever think using a broadhead that light is a good idea. However, it may be your only option, depending ont he variables I mentioned above.

Personally, I would always do the bareshaft test to see what weight tip will fly best, at what draw weight, and what arrow length. This is a dynamic process and changing one variable affects the others. The shortest shaft at the lightest usable draw weight will result in the heaviest head your setup will allow. You must test to find your answer. Otherwise guess, or take some stranger's advice and hope you get lucky.