325's by no means shabby. You must be doing something right to have gotten this far. How long have you tried switching it up? are you just mixing it up every other workout or are you strictly sticking to dumbbells for an extended period of time? Also be sure to mix up your rep pattern every now and again as well. To break out of my ruts on barbell bench I'll switch to strictly dumbbells for about eight weeks - focus on strict form and balance. I personally run something like a set of 12, 10, 8, 6, and 4 reps while increasing weight. Still hit incline, decline and flat. Your not going to be throwing up 325 with dumbbells so don't be concerned with impressing anyone as much as you are with form. Good luck 405s a pretty cool #.