Is it possible to just download all these CK kernel packages and do a upgradepkg ...tgz? Wont this break my system and dependencies and stuff? Or can I safely upgrade?
I would NEVER do an upgradepkg on a kernel!
these kernels should work well on your box but there is only 1 certain way of knowing.
use installpkg to install the kernel and modules, and the source if you need it. then run vliloconf or add the new kernel to your menu.lst for grub and reboot to test it.
Only then after you know it works and you like it better than the old kernel would I removepkg the old kernel and resetup my bootloader.