35mm would just be slightly lighter. Usually 40-55mm deep wheels have such a small weight penalty over ~30mm that its a no brainer to get the deeper wheels. Crosswind stability for wheels below 55mm deep is not much of a concern. Id don't think 9velo is a good value. I avoid many of these premium Chinese brands that are trying to compete with western brands. Price is double that of an OEM, and the product and support/warranty is the same, sometimes worse.
Calling it the same product is probably quite a stretch.
If you are buying from 9velo you are paying "premium" for the Hub. They use hubs from H-works which are really high quality. I haven't seen an OEM for a good price using true h-works hub yet?
For reference I've been using 9velo's mt30 MTB wheel for over a year, and they are perfect, best hub's I've ever used by far. Much better than DT swiss.
Also there are 10% off 9velo with youtubers discount codes. ex. 9velo-hambini10
So 872 usd including shipping for the 9velo isn't that bad
And for OP, I don't know how old your FFWD rims are, but modern rims has a more U shaped profile, where older ones has a V shape. The U shape is a lot better handling in cross-winds.