Have you heat treated this one.? I wouldn’t go any thinner on the tips now as it is as you’ll change tiller at this point. Only other thing you could do is add a sliver of laminated section on the tips belly area and narrow them a little but it may not amount to much increase if any. The fast flight string will help a bit but add tip overlays. Lighter arrows may cause unwanted vibration of unspent energy in the bow not being absorbed into the flight push of the lighter arrows. There’s a fine line of speed and smoothness. I just finished building a super smooth shooting sinew backed bamboo bow that shoots any arrow I fire through it well without any handshock. That’s not the norm though that Ive seen. I think the sinew backing may have something to do with this. This bow of yours likley shoots a well as it can given the piece of wood you had to work with.