hop and bucking "generally" will have very little effect on fps although from off to set will have a variance. Improving your airseal around the bucking (with PTFE tape) can give you a boost and will help with consistency too. Get a good air seal and see what it puts out then. If you still want higher fps you can run a tighter bore barrel or put in a stiffer spring. I'd not suggest going tighter than 6.03mm though.
For DMR rules, they are site specific, you need to ask where you play. Where I play you need to have I believe a one second delay between shots, this can be controlled with a burst wizard mosfet. You will never need to double tap someone, one BB counts as a kill, if you miss then you need to work on your accuracy as that is the point of the DMR/Sniper rifle roles. Personally the DMR doesn't have enough of an advantage over an AEG to be worth the MED or loss of burst fire and the delay between shots means you may as well go for a sniper rifle and have higher fps limits.