Commuter bike for better performance: less weight, or internal gear-hub? Background

I commute daily to work, the ride is about 10 km each way, across the city. The path is mostly streets with intersections, and a few long cycling lanes. Some hills here and there: Strava cycling app says 'Elevation Gain' is 80m.

I'm currently riding a Trek Valencia hybrid bike (2011), it's getting a bit old, and I'd like to replace it. I'm looking for the same kind of acceleration / responsiveness / sporty ride, but possibly getting me to make less effort to get the same performance (or get earlier at work).

Options

I want hydraulic disk brakes, good quality gear set, and rather an aluminum frame.

I checked what local bike shops recommend, and I'm now hesitating between two options. Unfortunately, trying the bikes is not an option, as no shop has them in stock.

Stevens Strada 900 (2019)

product page

It has quality components and is lightweight. I'll need to add mudguards and a rear carrier though, so it will be a bit heavier than the announced 9.4 kg.

Gears: 2 x 11 Shimano Ultegra R8000

Cube Editor black'n'purple (2019)

product page

This one looks interesting to me because of the belt drive. This would make the rides smoother, and avoid loss of efficiency in the long run.

Gears: Alfine 11 gear hub

Questions

I read posts with figures about the gear ranges of both systems, but I'm having trouble getting a clear picture. Some articles: stackExchange post, internal gear rations measurement, this post and that one.


How likely am I to get in situations where the speeds of the Alfine 11 gear hub don't switch correctly anymore?
Are the 2 kg less from the Stevens likely to make a noticeable difference in terms of energy efficiency?
Will any of the bikes above provide a range of speeds comparable with what I currently have (mid-end 3 x 8 derailleur)? I had the opportunity to try a bike equipped with a Shimano Nexus 8 gear hub, and there were definitely not enough 'high' speeds. This would prevent me from riding fast enough on flat lanes, or downhill.


Or to summarize, perhaps: more lightweight bike with derailleur or Alfine 11 gear hub, which would you recommend for my use case?

Any input and tips appreciated.

Thanks,

P.S.I also read the answers to How to improve my performance on a commute? and will probably follow some of the recommendations in there, like getting clipless pedals.
When you use your bike every day, reliability is as important as weight. 
I use 2 bikes, with a train ride in between. The bike I use at my work town rarely gets maintained. I take it home 2 times each year. The only things I do regularly is pump the tires and lubricate the chain. Even then it keep riding as good as new. The derailer bike I had here before that needed a lot more care.

The things I learned over the past years:


The simpler the better. If the terrain is flat enough to get by with a bike without gears, do so. 80m elevation is on the edge, and depends on your physical condition. If you feel the upper gear on a Nexus 8 is not large enough, you're riding quite fast (35Km/h+) already. I ride a bike with an Alfine 11, and have no problem doing 35 in 8th gear. Another thing is adjusting your style to spin faster (85+RPM), which generally is also better on the knees.
No front shock absorber. The good ones are too expensive, and the other ones too heavy and crap
No V-brakes or cantilever brakes. At least hydraulic rim (Magura) or disc brakes
Mudguard!
A rack to hang bags (I am very happy with bags like this). No backpacks for me.
A IGH is a lot more carefree then a derailer.
being able to shift at red lights is very handy
The lights have to be driven by a dynamo and fixed to the bike (battery lights get empty or forgotten at the worst possible time)
No NuVinci. It is heavy, and you can't shift when stationary


So I would not use either of the bikes you suggested, but something like this or this

I don't have an opinion on chain vs belt. My girlfriend has a bike with a belt, and that tends to stay cleaner then the chain on my bike, but I don't know whether it is worth the extra expense.