So, will they last or best stick with steel?

Looking at this.

14 and 18t combo which would suit my needs but it might be too soft.

There’s a reason the smaller cogs on cassettes tend to be made from steel 😉

I used a 17t Chris King – unfortunately it didn’t last long… Not really an area for weight saving in my experience.

Thanks. I’ll stick with steel.

Got one of these on my Stormchaser

Endless Bike Company Kick Ass Cogs

Try here, used to use these on my fixed gear road bike and they were fine.
https://www.velosolo.co.uk/shop.html

They last about half the time of steel (at best) and usually cost about twice as much so overall cost about 4 times as much for same mileage. You will save 20 grams though…