After about 10 years of driving in scandinavian winter conditions with old Africa Twin RD07a (750ccm, 240kg) and DR350/385 (135kg) my opinion:
Snow
Once your tires move through not compressed snow, you need something, that "bites" into the snow - imagine shovels. That's the point of time, where rough tires come into play. Deep profile and space between so they easily clean themselves and "bite" into the snow. The bigger the studs, the better. That's where MX-type-tires like Mitas XT, Dunlop GeoMax, Michelin AC-10 and the like shine. At the same time otherwise pretty competent universal tires like K60 or even worse TKC loose out to the point one can't make it up the road to reach the top of the mountain (and even if, it's a pain with feet down to the ground not to sink the ship).
The spikes themselve don't play any role here (they come into play once the bottom is compressed - like hard snow or ice).
Ice
Here the tires won't matter. It's only about the spikes that "bite" into the surface of the ground. No spikes and you'll go sailing, skipper. The heavier the bike, the higher the speed the bigger the chance of loosing control to the point of no return.
1.200 allows you to drive slowly on ice - carefully. No fun.
1.500 is the compromise between letting it fly, hitting the occasional tarmac and not having that much of rubber tire-wise available to screw them in - in my eyes best compromise for every condition once you have to plan to also hit the black tarmac
(1.600) bit shorter top and bottom - perhaps good compromise if 1.500 is to long threadwise - see
here
1.800 the weapon if you're only in for having fun and never hit the tarmac AND have enough rubber available to screw them in
For the amount of spikes
If you take it slowly, you don't need to many. The far sides might even be ignored. But if you plan to let it fly, you should even put spikes into the very outer studs - if you have none there, you might expect interesting drift-effects up to spinning a motocycle around the own axle. I twice checked it out on playing to hard...
Last winter i had to change my Mitas XT 454 green after not even 1.000km. The Dunlop Geomax MX3S soft afterwards got 2 1.500 Spikes into the middle and every outer stud got a 1.800. And boy! The bugger pushed as hell! Traction without end - even with to much air in the tire.
Big bummers
If you drive a big and heavy bike - especially with 17" back-wheel, your choices of tyres are limited. I'd suggest to choose the ones with the most aggressive, deep, open profile - and i'd say, K60 are NOT open and agressive enough. Especially on the front, K60-profile does not provide enough depth of profile to bring in bigger spikes - probably not even 1.500 (i'm not sure).
Come to TKC80 and i really, really would suggest, NOT to use them. Had several situations with friends using them on their big bikes (Stelvio in summertime) and they provided MUCH less traction (to wide, to flat blocks) and were punctured several times during a 10.000km trip while the K60s were not hit once. During the Fjordrally an italian 1.200er GS drove on TKC80 and he had to stay in the valley as he couldn't make it up the mountains due to the TKC80 which didn't provide enough traction on hard snow. His 1.200er spikes (longer didn't fit in) where no help either in that situation.
For the really big bummers - 200+kg, GS, AT, ... - the amount of usable tires is not very good. K60, TKC80 - not enough snow traction. Perhaps slightly better AX41. On my AfricaTwin i drove the Mefo MX-Master and Stonemaster. For heavy bikes perhaps the best available (although - as Björn mentioned - quality seems to have decreased during the last years). Didn't see: Jörg's mentioned Mitas C02 look good (forget your official tire dimensions - if they fit, fine). Remember: Don't buy those tyres as you would buy tires to drive on the streets, the black tarmac. Buy the tires you'd use to ride your bike heavily through the biggest and hardest dirt, mud and whatsoever.
Also keep in mind: Don't use the tires before you've put in the spikes. The rubber-height of the studs/profile will decrease significantly on the first 100-200 kilometers. Even on short distances perhaps that quick you don't have enough flesh left to put the spikes in.
A side-note: My tyres read "not for highway-use" and i've never seen that letters ... somehow. What's good in the deep dirt, is also good to drive on snow and ice (of course with heavy bikes different story). Just add the extra security of spikes.
2nd side-note: If the tires are too extremely soft, the rubber will bend with the torque applied between tire and ground (tarmac, ice). Once they bend, the soft-side of the spikes are hit. Not good. Slightly soft tires alright. Too soft - not good.
3rd side-note: With spikes - especially heavy bikes - become wobbly. Take it easy. Let it wobble. If it's to much, decreasing the air-pressure in the tire slightly, might help a lot. If you need max-traction up a hill, the same. But lot less pressure and tire-holders.
Good luck.
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Which ferry do you take to go to scandinavia? I think to remember, that in Kiel (Colorline Kiel-Oslo) pretty close to the ferry-port (on the way to it) there was a possibility to store tires. With a bit of time you could drive there, change tires and do the last 500m/kilometer with your mounted spiketires (expect them to surprise you a bit...
). A.T.U. might have been that shop - worth a try:
https://www.google.de/maps/place/A.T.U+ ... 10.1390867
,like a Africa twin or a GS, and have good results.
