You might consider measuring your chain later.  The cheap small chain checkers are not very accurate, but you can measure the length of an entire chain when it hangs from a hook.  One link is a half inch when new, thus 100 links is 50 inches from center of pin to center of pin.  If it is 50.5 inches, that is one percent elongation.  I think on a Rohloff bike replacing the chain when you are a bit over one percent elongation is a good time to replace it.

In case you were wondering. Assuming your method is correct ( which I am), and my maths and measurements are correct ( which I am less certain of) the chain is at ~1.8% elongation.
 

I have tried various motorcycle lubes at times in the past. Anything that worked reasonably well on a bicycle chain in wet weather also picked up a lot of dirt, so not good on an exposed chain. It might be different under a ChainGlider.

I think that the motorbike chain lube you have quoted would be fine on a modern motorbike chain, which is what it is designed for, keeping the side plates rust free and the roller / sprocket interface lubed - but I don’t think it would get into the rollers of a cycle chain.

The technical data sheet for MOTUL MC CARE C5 Chain Paste says "All types of chains: standard and with O-RING, X-RING, Z-RING.", so I'll give it a try.   

I have one motorbike with a chain (I prefer shaft drive) which is a low powered 411 Royal Enfield Himalayan, used on and off road.  The chain is the OE one with O rings but I have fitted a manual chain oiler to drip ATF fluid onto the chain to ‘wash’ dust off.  I have tried using heavier gear oils but they do not clear the dust - ATF is very thin.

My brother has a Scottoiler system on his off-road motorbike. This drips oil (Scottoiler brand) onto the chain. Works for him, but not on a bicycle (I tried).

So personally I now use a thin ‘wet’ cycle oil on my 2 bikes that have chaingliders and drip it onto the rollers.

I do the same on my own bikes when the KMC factory lube has worn off. Quick and easy to do.

But dismantling/refitting the ChainGlider can be challenging for a user with no mechanical aptitude.

Under a ChainGlider the slightly sticky factory lube on KMC chains works for a long time, but after a lot of use in salty and/or wet conditions it eventually needs renewing with something. So I need something that lasts for a few weeks even under very wet conditions.

...
Motorbike chains are different to ours as they have O rings keeping the original lube inside the rollers - and dirt, water and chainlube out.   Motorbike chain lube is more to lubricate the roller / sprocket interface.
Personally I think a thinner chain oil is better on a cycle chain so it can seep into the rollers (no O rings).

I had not thought to compare bicycle chains with motorcycle chains.  My old Triumph motorcycles has a chain oiler, some of the engine oil (20W50 during most of the year) dripped on to it.  Thus, I never oiled it.  And half a century ago, there were no O rings in chains. 

I suspect that as the chain that was wrapped around the counter tooth sprocket inside the gear case at highway speed, any dirt that was not hanging onto the chain really tight got flung off of the chain at speed.  I stopped driving motorcycles a decade and a half ago.

I used to use a petroleum based lube on my bicycle chain, ranged from 20W50 to 90W140 gear lube, but it was a dust magnet.  I switched to a wax based lube about a decade ago, very happy with that. 

First attached photo shows my big chainring at the end of a tour with a lot of accumulated dust and dirt, that was shortly before I quit using a petroleum based lube.  The chain was on the middle chainring, thus hard to see the chain in the photo, but it is very clear how dirty the chain must have been for the big chainring to be that dirty.

I mostly ride my derailleur bikes, but I do not use a Chainglider on my Rohloff bike either.  I have no complaint with dripping on some wax based lube on a regular basis.

Second and third photo from a year ago, a very dusty day on a gravel trail with my Nomad Mk II.  I rode 90 miles that day for exercise, the attached photos were middle of the ride.  The chain is clean enough in my opinion, a lot cleaner since I switched to the wax based lube.

I do not try to keep track of how many miles I get on a chain.  I regularly ride four or five bikes a year. 

‘At the moment I just use an oily wet lube on the chain when the manufacturer's lube has gone, but I might try a chain grease advertised for motorbikes. I tried that in the past on an unprotected chain, but it picked up a lot of road dirt so it was worse than an oily wet lube, it might work better than an oily lube under a chaincase’

Motorbike chains are different to ours as they have O rings keeping the original lube inside the rollers - and dirt, water and chainlube out.   Motorbike chain lube is more to lubricate the roller / sprocket interface.
Personally I think a thinner chain oil is better on a cycle chain so it can seep into the rollers (no O rings).

A better scheme if you want to get maximum miles for your money, for when you ride from home, not on tours halfway around the world, would be to have all the chains you expect to be consumed on one side of the sprocket/chainring to hand, and to fit them in order at some routine event (a distance, cleaning the chain, whatever), so that they can all wear in evenly with the gears. It has the advantage that you don't need to know with high precision how much wear per chain is optimal, you just spread it across all the chains and the metal will tell you when the limit is reached. Martin has written about this method, though not in these terms, and I think JohnR has mentioned it too.

It was worth it for me with derailleur transmissions. The simplest way was with 2 chains, take the chain off when it needed cleaning, put the other one on, then clean and lube the one taken off ready to go back on the bike at the next change. Generally at 300 to 500 km intervals, but very weather dependent. The best I managed before having to replace the cassette was with 4 chains.

Still worth it on my Bromptons - the exposed transmission close to the ground picks up more muck than on a large wheel bike.