For a 3 cross wheel Spocalc suggests 261.3 260.4 for a rear 135mm FSA Phil Wood hub and 221 Mavic MTB rim. DT Swiss seems to produce even numbered length spokes. Should I buy 260 mm or 258 mm (258 assumes the spokes stretch during tensioning) spokes or both lengths.

Also Phil Wood sells the FSA in 36 deg, 40 deg, and 48 deg. I think 36 is for MTB wheels but am not sure.