X-Plane's texture set is 1.4 Gb, but that doesnt include mesh or other items. Install the OSX OpenGL Driver Monitor here: http://cdn.isdg.com.au/~chrisk/OPENGLMONITOR/ Enable the "VRAM in use" graph, and it'll tell you how much VRAM youre *actually* using. I suspect that OSX is seriously hitting the VRAM hard, and the extra clouds are "pushing it over the edge". I did the same test on my GTX670 and found that I was indeed exceeding 2Gb of VRAM, even though XP10 reported only 1.5 Gb. - CK. EDIT: Let me know if that .DMG doesnt work, as thats the XC6.1 Yos Build. I have access to the previous versions (mavs/ML/etc.)