I went from 170mm cranks to 165's on my Europa and it felt like going up a gear as far as effort goes. Mind you, since the change I've been spinning quickly and smoothly but that might because fitting the new cranks coincided with me parking the geared bike and moving exclusively to the fixed. Now that I'm trying to climb decent hills, I'm wondering if going back to 170's mightn't be a good move for the extra leverage going up.

There's really only one way I'll ever know - try the 170 cranks and, unfortunately, I would suggest that the same answer applies to the OP.

On a related note, my geared bike had 172.5mm cranks, the Europa at that time, had 170's. I always felt just a wee bit cramped on the geared bike, dunno why, can't explain it, just that little thought that kept popping into my head. The geared bike had octalink cranks that went the way of all octalink cranks ie, they refused to stay tight, so I had to buy new cranks and, seeing I was buying new, ordered 170mm cranks. I could detect no difference in effort ability to spin, but I no longer had that nagging feeling that I'm cramped - instantly more comfortable.

Maybe there's a similar subliminal thing going on with the Europa and her new 165's.

Some aspects of bike fit come down to how it feels to the rider ... on that bike. This is why experienced riders who tinker with their bikes (as opposed to living with what the factory delivered), wind up with a shed full of bits.

Richard