The answer would be bandsaw or power hacksaw, unless the cutting needs to be done while standing on a ladder or some other unexplained situation.
The motor power in a reciprocating/Sawsall saw isn't easily applied to the blade at the cutting zone, so motor power isn't a major factor in this case. Both the bandsaw and the power hacksaw cut much more efficiently (and accurately).
The power hacksaw at least lifts the blade away from the workpiece as the blade is retracted, which a recip saw doesn't do.
The recip saw doesn't offer any load/pressure to the blade cutting force, and the forces that are generated are actually counter-productive to cutting efficiency. The vibration doesn't contribute to cutting, but instead, counters the cutting force due to overall shaking which makes the cutting more difficult for the operator. Since the blade generally stays in contact with the workpiece, the recip saw is attempting to force the saw back at the operator half of the time.
The length of the cutting stroke, and the speed of the blade, would be of more significance than the difference of a couple of amps of motor power.
When cutting wood, a recip saw is sometimes faster than trying to use a handsaw, (due mostly to strength and stamina) but certainly not as efficient as using a circular saw, for example. A recip saw offers better access in many cases.
The lower speed required for steel and other metals will require more of the operator's time, while realizing just how slow it cuts (and lack of control). Increasing the recip saw's speed will most likely reduce the cutting efficiency, and dull the blade.
Cutting thin metal stock will likely be more problematic.