RE: 60 or 70 lb bow
Personally, I would ignore any efficiency advantage. It would be minute at best. It is always preferable to shoot the exact poundage that matches your arrows spine perfectly, rather than a number based on bow efficiency.
I always try to shoot an arrow that lies in the middle of my bow's draw weight range. This gives me some leeway to adjust poundage up or down a bit to perfectly match the arrow. If 60 lbs is the max you'll shoot, I'd recommend trying to get an arrow that will spine at 55 lbs with your draw length, arrow length and tip weight. This gives you room to go up a few pounds without exceeding your maximum draw weight.