Originally Posted by prooftheory

There are a lot of different factors here. You might be perfectly strong enough to push 44x16 but not actually have the endurance to keep going for that long. In this case the solution might be to gradually lengthen your rides. If the 15 or 16 mph average you gave includes stoplights and whatnot, this might also be affecting whether you are comfortable. Since you already have a 44t chainring I would go down to it and see how it feels and then buy some bigger cogs and see how they feel. Cogs are relatively cheap and easy to change.