Well its probably been discussed to death on here but what length do you ride on an MTB ?
I need a new chainset and I'm measuring out at a 33" inside leg which from all the common internet wisdom that would suggest a 170 crank.
I don't worry about it that much. 175s and 170s, can't tell any difference. Reasonably sure the Ragley has 175s and the Hemlock has 170s but honestly, maybe it's the other way round.
DH bike needed 160s so I could pedal it though- kept kneeing the crowns when climbing on 170s 
Yes I suppose you would notice what is 5mm I have 175 on all my MTBs but have chance of a bargain XT chainset at 170mm, which is suggested is the right length for me anyways.
Just under 32" inside leg, have both and don't really notice the difference.
170 is likely OK but probably 175 would be 'better' for you.
Well after carefull consideration I've decided on the 170s £84 from Merlin for XT
