bluefoxicey. From what I've read and experianced in decades of riding a bike, the crankarm length is the most easily adaptable cycling related item for the recreational rider to become accustomed to, barring range of motion issues. I read excerpts from a study that proclaims that 170 mm is the most suitable length for most recreational riders. My four roadies have four different crankarm lengths and I can tell a difference if I ride them back to back, but then I quickly adapt.
Cadence is perhaps the main issue. A shorter crankarm is more suitable to a cyclist that spins, or wants to spin at a higher RPM and the longer crankarms are a good alternative for those that spin slower, producing a tad more torque.
All-in-all it won't hurt anything to try the 170 mm length crankarms.
Brad