When I get around to fitting the narrow/wide chainring, either a Superstar, Race face or On-one it’ll more than likely go on some XT/Deore cranks so do I need 6.5mm length bolts?

Get a one up components ring, it comes with bolt spacers so you can use your existing bolts. There was 20% off to just before Xmas as well.

I’ve just used the bolts that came with the chainset (xt/lx) for RF & hope NW rings

Oh right cheers hopefully it’ll be the same for me. I just checked and I’ll be using either a 30T on-one or 32T superstar chainring.

I have used a On One Ringmaster, just reused the bolts that came off my triple crankset. Although I recently changed to a superstar N/W chainring and it was thinner than the Ringmaster. I used short chainring bolts with this one.