[Xack]

Smaller diameter can make for better clearances and things look nice under the hood. However, the smaller diameter will twist under torque. you will have stressing things like welds on the knuckles which... you cannot determine if they are good or bad by looking at them. The trade-off for a larger diameter steering knuckle is only a little more space for clearance. For your heavy front end, high HP car it's your choice. For me I'll take the larger size components with good mechanical assembly for peace of mind.
Power Steering does reduce the stresses on the steering components from the rack back to the wheel.