So - couple things.
First are those actual speeds, or estimates based on IBO? Looks like an estimate, so you're probably running slower if I had to guess. Looks suspiciously like my Hoyt CD Turbo - and my actual IBO speed was around 335-340 and we have the same DW/DL. I was on the #3 cam.
If you're actually running that fast though, I prefer more weight. I settled on a 505gr arrow and get around 285 fps.
Having done the D6 all last season - , if you're committed to staying with the 4mm arrow I would use 125 grain heads. If you need more weight - either add another insert to all your arrows for a little extra which keeps your hunting and practice arrows the same, or build new arrows and tap the backs of the inserts for GT FACT weights. You'd need to insert them from the back of the arrow. Depends how committed you are to 4mm arrows - you can build 5mm arrows with a brass insert and use standard thread broadheads...