RE: 85 grain, 100 grain, 125 grain
These are several factors to consider when deciding on head weight. You want the best weight for your set-up.
The head will need to keep you in the correct spine range for your set-up, and give you a good FOC (front of center) approx 9%-13% is a good range for hunting in my opinion.
Sometimes a couple of the different weights will accomplish this then it comes down to what weight flies better and personal preference.