It really comes down to how much time do you have to play. Are you the guy who has a full time job, wife and kids, and needs to maximize his time for most gains possible? If so, hold on to those weekly bounties so that you can get max benefit from them as the weekly tempered buff gets stronger. It is quite possible to rank all the way up to 5 in the last day or two of IB just by playing a couple hours and turning in those weekly bounties. However, if you are they guy who is going to dedicate 2-3 hours a day playing every day during IB week, it's best not to wait on anything. Your gains will be maximized by playing at a higher rank for a longer period of time, thus dramatically increasing your potential to get IB weapon/armor drops.