I'm looking to change the stem on my road bike for a white one to match the new bars, exceptional tartage I know.

THe stem in question is a FSA OS99 with Ti hardware & 31.8mm clamp size, will this be suitable for mountain bike use as it's very light at 111g's or am I asking for trouble?

The reason for this is I think it would be a shame to sell it for some crazy knocked down price. It's a good 60g's lighter than the Sunline V1 AM on there at the mo.

For general XC use I'd have no hesitation. If you run a wide bar it may be a bit twisty mind.

Is the OS99 the same length as the Sunline? I thought it'd be 120mm or so and the Sunline 80mm or less. Also wouldn't the Sunline be on a long travel bike and therefore the OS99 perhaps less suitable?

The OS99 is a 90mm stem, the sunline is a 65mm stem.

I fitted the sunline when I built my Nicolai Helius up as it's what I had.

It's a 130mm travel bike BTW.

Maybe I'll get a Raceface Deus or summit similar

I'd have no problem in using that on a (proper) xc bike.
If FSAs usual standard of weight claim is in force, it'll be nowhere near as light as claimed anyway.

If the bike is good with a 65mm stem then it'll be like a barge with a 90mm one. The OS99 would be more useful on a 80 or 100mm XC hardtail – that's the length I use on both my Zion and Epic.