high/ultra is max... I'm saying this for future games as well, the ones that will be vram hungry. 4GB should be enough, 2GB won't be enough for certain games but as you wish.. Check the prices, if the price difference isn't too big between 2gb and 4gb version I'd take 4GB. Also xfx isn't that good GPU but I guess it's the cheapest brand on the market so if you're on a budget then ok
PS: If you must choose 2GB then I'd rather buy R9 280X Dual-X or Tri-X Toxic Sapphire are best models, but even XFX model will be faster than XFX R9 380 2GB