Howdy arche3,
I am running the 8GB 5500M, but wanted to chime in with some important amplyfing information. The GPUs that Apple are using in the MacBook Pros, are Radeon Pro branded, which means that they are not optimized for gaming. They are optimized for compute work and workstation use. At a hardware level, they are very similar to the standard Radeon cards, with the real difference being the drivers. Under Windows 10, Radeon Pro cards do not perform as well as standard Radeon's under gaming conditions (Warzone or whatever), but this does NOT mean they will perform badly, just not as well. It seems many folks use "red" or "blue" drivers from a third party under BootCamp, as Apple does not keep the drivers up-to-date under, and as there is no direct laptop Windows analog for the Radeon Pros used by Apple, you will get mixed results with drivers downloaded from AMD. With my new 16" MBP, I have elected (at least for right now) to NOT install BootCamp, and to try and keep my gaming relegated to macOS. Which is really only 1 game, Diablo 3.
Regardless what you want to do, a comparably equipped Windows PC will play games better. For Diablo 3, it is "good enough" for me at the moment
Rich S.