For the Middleburn RS7 to sit equally spaced between DS and NDS, it ideally needs the symmetric axle.
A 110mm is 3mm longer on the NDS only compared to a 107mm; not 1.5mm each side. An old trick for a 110mm is with a 1.5mm / 2mm spacer under the DS cup. Since the shell width is extended, the NDS will need to be wound in more. The shitty plastic NDS cups can not be used, but the metal ones can.
[ all my references refer to Shimano square taper just for clarity, many people are not that bothered about this symmetry difference in practice]
EDIT: If you have tried with 113mm already, check crank arm clearance and ring clearance and make a judgement call to use a 107mm (3mm less each side).
A 110mm is 3mm longer on the NDS only compared to a 107mm; not 1.5mm each side. An old trick for a 110mm is with a 1.5mm / 2mm spacer under the DS cup. Since the shell width is extended, the NDS will need to be wound in more. The shitty plastic NDS cups can not be used, but the metal ones can.
[ all my references refer to Shimano square taper just for clarity, many people are not that bothered about this symmetry difference in practice]
EDIT: If you have tried with 113mm already, check crank arm clearance and ring clearance and make a judgement call to use a 107mm (3mm less each side).