What's your height, inseam, etc?
Longer cranks are definitely worth trying, but whatever
you do, if you increase your crank length by 5mm or more,
you have to ease into it. I went from 170s to 175s, and stuffed
up one of my knees, and it took a year to repair.
So, you have to give your
knees a chance to get used to the increased flexion at the top of the pedal stroke.
The standard advice goes like this: longer cranks give you more leverage (torque), but they are more difficult to get "spinning" quickly, therefore, sudden accelerations may be affected.
With longer cranks, you're more likely to hit the ground with your pedals.
