The R5 is a better case in many aspects, but both cases are good.

The Define S offers a wider compatibility with liquid radiator setups, but since you're using the H5, that's not a big consideration.

Either case will house the GPU without any drive cage interference. The R5 is the more limited one in that sense, offering up to 310mm long cards before interfering while the S offers up to 425.

The most prohibitive difference between the two is 5.25" optical drive bays. The Define S offers none, but the R5 offers 2 bays. So if you want to put in an optical drive, the R5 would be better.

Overall, either one is fine for what you're doing. Your build should stay quiet based on the parts in it, but if acoustics are of extreme importance, the R5 does offer slightly better sound dampening.