Much to talk about here.
First, it sounds like you've go the itch for a new bow. I can understand that. I'm not up to speed on current one piece bows, so will wait to see what others have to say.
As far as broadhead performance goes, momentum is your friend. Your current setup has lots of momentum with a hefty mass component. A well placed shot with a sharp BH is going to go right through deer sized game. Don't get caught in the speed equals more energy trap. You could easily switch to a lighter, faster arrow but it's not going to give you more energy and probably would be less. At least your lighter arrow would lose energy quicker. If you want to see what difference a lighter arrow would make with your current bow, you could easily drop to around 400 gr and still have a reasonably heavy hunting arrow. I agree with Steve that a string change could add some more speed. Maybe 5fps depending on what you are using now.
Last thing to mention is that you could look into different limbs for your Discovery as it is ILF. Mediums would shorten your bow to 60". A good hunting length for your DL.