I'm no pro on this. But a few shop owners have told me that if you have a choice between the 2 you are better off shooting a bow at full poundage than a bow set to lightest poundage.

As for speed. I could and may be way off on this. But I would think that the fully loaded 60 lb bow would be a little faster. The limbs are cranked the whole way down on that bow while the other bow the limbs are cranked to a lighter setting. Yes, both are 60 lb draw but I would think it's the way the each bow unloads that is different.

So, maybe it's a matter of which one transfers KE better?