IMHO max power doesn’t mean much for touring. Max power is achieved on high RPM, which we barely use. (Typically around 7500-8000 rpm on a twin).
Max power is usable on the pub, not when touring.
What I think matter is how the engine works at cruising speed, one way to look at this is to look at the torque-chart. Normally you would find that maximum torque is at rpms above your cruising speed.
Acceleration, weight and torque are directly linked. If you double the torque and the weight on a bike you will still have the same acceleration (in theory, and it’s not far off as long as you compare reasonable speeds).
If we compare the DL650 and F800GS we will find that they both weigh 222kg (at least that what they found when they weighed them in a magazine).
If we say that typical cruising speed (4000 RPM) we will see:
DL650: 52Nm (tourque/weight=0,23Nm/kg), at 4000 rpm
F800GS: 68Nm (tourque/weight=0,31Nm/kg) , at 4000 rpm
That means that if the bike has the same gearing you will have 30% more torque available on the 800.
This difference gets a bit smaller through the rev-range, but not much.
If you look on acceleration (60-100 km/h top gear) you will see
DL650: 6.0 Sec
F800GS: 4.7 Sec
The 650 is 28% (ca 30%) slower then the 800 so the theory seems to work, okay?
We have not seen on the weight yet, because the bikes have the same weight so it doesn’t matter. But if we introduce a heavier bike 1200GS, we will see:
Weight: 235 kg
Tourque: 92Nm (tourque/weight=0,39Nm/kg) , at 4000 rpm
Okay, so the 1200 have 25,8% higher tourque/weight then the 800. This is without driver and luggage, so we add 120 kg.
The difference in torque/weight increases to 30%, which is almost 20% gain in favor of the 1200.
This shows us the bike with high torque suffers much less from the added weight then an engine with lower torque.
If you repeat the above with a 650-single you will find that it suffers a lot from the added weight because it has very low torque at cruising speeds.
Funny enough the max load is identically on the two bikes, which means that you are allowed to carry more luggage on the F800GS.
On the other hand I’ve ridden both bikes and I would rather prefer a 150 kg load on the 1200 then on the 800.
Does this matter in the real world?
As stated before on this site it’s possible to tour the world with any kind of bike. It’s also possible to live your life in seclusion. What fit’s you it’s up to you.
A bike with high torque will normally have a bigger engine (twin) and a sturdier frame then a bike with lower torque. It will also carry it’s load better, both in the aspect of engine-wise and frame-wise. The drawback is that it has a higher weight, but the weight is only a problem if you can’t handle it. You can learn to handle the weight or you can drive a lighter bike, it’s all up to you.
This is just some thoughts, a lot of other factors are important. It depends on you and your trip, well mostly you because you can go everywhere on any bike.
All numbers above are meant as indicators to show the physics. Calculations are made around 4000 rpm and the gearing should be more or less the same.