I've noticed it, too. I find myself disabling shadows in general now, whereas in the pre-247 builds, I could run it with shadows. I don't know what what's happening, but performance certainly doesn't seem to be getting better.
I'll just chime in here and offer the perfect solution to the whole hopping whenever attacked by skulks thing -- Make the marine's weapon either totally useless, accuracy-wise when jumping, or make it actually useless until he's on the ground again.…
The performance is making it hard to enjoy the game. Gameplay additions, maps, features, all of these comes come in second compared to the low performance you get. The game as it stands just barely deserve…
Keep the jumping, but make shooting impossible or wildly inaccurate while you're in the air. This shouldn't be a thing, and that's how I think it should be solved.