33s are fine if you never actually ride on rough gravel or loose dirt. But I would go with the 38s to open your riding options. I have 40s on my gravel bike and I’m very happy with them. So much better off road than the 35s I have on a different bike. I must caveat with “I know nothing about CX”. Strictly a recreational riding perspective. I find the 40s very smooth on pavement and can’t imagine that they are any slower than the 35s in that regard (I’m not road racing anyone on my gravel bike). And I can ride non-technical mountain bike trails easily with the 40s…a bit more sketchy with the 35s. I guess I’m in the camp of “fatter is better” these days based on my own non-competitive road and gravel bike experience. So the 33s could fit the bill if you are confident in your riding environment, but I recommend fatter if you want a wider aperture of riding options for this particular bike.
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