I have Gothic running on Win 7 x64 with player kit 1.08 and system pack 1.6 installed, default keybinds. My problem is in the starting area, by the derelict mine there is a ledge you are supposed to be able to climb. Every time I jump, I get pushed backwards. I have heard this is due to the uncapped framerate. I have a 165 hz monitor. I tried setting it to 120 hz and vsync half refresh rate (60 hz) but nothing seems to work. I tried limiting the fps with riva tuner, but it always seems to be at 120 hz or more. I tried the "Marvin" mode F8 to jump, but this is really immersion breaking and usually sends me off a cliff. Any ideas? Thanks.

Where exactly are you trying to climb? Are you sure you're supposed to be able to climb there? There are a few places in that initial area that are just a bit too high. Usually there's another way to get up where you want to go.

I say this because a few weeks ago I finished a playthrough with the same setup you're using, and I never had a problem.

Just finished Gothic I with the same setup and OS. Noticed this problem almost immediately. I've played the game many times before, but not on Win7 and without community patches and everything was fine. Now climbing is almost completely broken.
Game determines if you can climb before you jump. If you can, your camera will shift upwards. There are places where you could never successfully climb despite the camera shift, but they were rare and they looked the part.
After doing full playthrough I can recall about 3-4 times when my character actually managed to climb after looking up. Even climbing relatively low obstacles like from lower "ring" of the New Camp farm to the upper ground (Barn level) was successful in about one in a dozen attempts.
Climbing anything higher than my character proved impossible no matter which angle I tried.
So no, it's a real problem, not a misunderstanding on a player side.

Not sure if it's related, but I also noticed that my NPCs do not sleep. They go to bed when it's late, then immediately get back up and sit on a chair through the night. The whole Old Camp did this. Wasn't paying attention in other camps. Interestingly, if I reload a save while near a hut, people would go to bed again, then immediately get back up.

Install the SystemPack. I play with the FPS patch as well and I have no problems. Some higher areas you're not supposed to climb, anyway.

Did you read the OP?