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I've only sailed in 40 knots once. Lots of times in 20-30. But in that 40, I felt the exact same shuddering you're talking about.
However, I was under double reefed main only (doused the hank-on 110) and stayed off the wind quite a bit (beam-to-close reach). This let me control the shuddering by easing off the main in the gusts.
Definitely spooky though.