So I finally did it. Results?
First was unable to shrink in windows due to a bunch of reasons, but I overcame them: hibernation file, page(r)file, and other bullcrap.
Finally, I could shrink. Then, a fatal error in the shrinking process. I ignored it. Waited few minutes and the disk seemed to have shrunk after all. Weird.
Then proceeded as planned. GParted the rest. All is working fine now!
Moral of the story? None.