What are the key factors to consider when determining the ideal crank arm length for a Raleigh Militis 3, and how do they impact performance and efficiency for riders with varying leg lengths and riding styles? Would a shorter crank arm length provide a better power-to-weight ratio, or would a longer crank arm length offer more efficient energy transfer and reduced fatigue on longer rides? Are there any specific crank arm lengths that have been optimized for the Militis 3s frame design and geometry, and if so, what are the benefits and drawbacks of each? How do professional cyclists and bike fitters approach crank arm length selection, and what are some common mistakes to avoid when choosing a crank arm length for this bike?