Should you install GPU drivers on HDD or SSD

SSDs have a limited number of program/erase cycles per cell, in the order of 5000, depending on the drive. The controllers in recent drives "rotate" these cells to spread writes across the whole SSD, maximising the life of the drive. There is also hidden, spare area which can be used to replace cells that have worn out. In theory, it is possible to read data even after all program/erase cycles have been exhausted. So the likelihood of losing data due to the drive reaching the end of its lifetime is small.

Nevertheless, the drive's controller hardware/software may fail (which I think is what is described here), rather than the flash memory. This is clearly difficult to predict, but historical failure rates suggest that some manufacturers made more reliable SSDs than others.

Games can take a lot of space, and, as you point out, an SSD will largely only improve loading times rather than in-game performance. There might be a noticeable improvement for texture-heavy games, if textures are loaded from disk on-the-fly. SSDs tend to be faster the more free space that is available, so filling the drive up with largely static data such as games is generally not advised. I'd say it's a matter of personal preference - you might want to have a couple games on an SSD, and all others on a hard disk.

A solid state drive only improves disk I/O speed, i.e. accessing, moving, editing... files. Once the game loads, it's entirely up to the RAM, GPU and CPU. Installing your games on a SSD will only make them load faster. I'd advise you to partition your SSD to have both you distro's system partition and Windows' system partition on it, since the system is constantly accessing files.

I'd also create a data partition on the SSD to store documents, music, video and other files I constantly need to access, since they'll load faster on it then they would on the HDD. Creating a data partition is a good idea in your case because it can be accessed from both operating systems.

As for the HDD I'd use most of it's free space for Windows, since games take up a lot of space. The remaining free space I'd leave for the GNU/Linux packages you may install - keep in mind your personal files are on your data partition on the SDD.