What are you running at the moment on your (road) bike? I think comparing it to what you have is a good idea.
I run 42 - 11-42 on my gravel wheels and a 10-42 on my road wheels. The 10t cog really makes a difference on false flats/downhills when you want to keep pushing a bit - I wouldn’t say you need it for speed, for me, it’s rather to keep the pressure on the pedals and stay in a training zone on (straight) downhills. Personally, I like the simplicity of 1x. I know some people dislike the gear jumps. With a lot of rolling terrains and a lot of stop and go I quite often shift a few gears at a time - even on 1x… 
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But coming back to your question: If it’s gravel races I doubt that you even need that 10t cog. At least to me it’s hard to imagine on gravel at 50km/h feeling the need to speed up instead of just aero tucking and trying to keep control 
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