For a clearer explanation, here's a basic reflective surface baked with 18 and 2 reflective samples at 512x512, downscaled to 64x64 to get edge antialiasing. (8x oversampling) The one on the left looks hardly any different, and took 8 times as long to render as the one on the right. If you're going to oversample to get…
+1 on it being a bit slow as well. I'm currently using Blender in a diffuse-only pipeline and it's not terribly quick. Reflective surfaces in particular are killer. However, it's best I find with baking in Blender to do a 2-8x oversize map and downscale as you said to get AA, but also take that into account with your…