The issue is not that bigger textures are not supported, it's more that bigger textures are slower. Compare render speed with two 1024x512's with the same scene using four 512x512's and see which is faster. I don't know, but I have found some odd anomalies with this, like being able to render nine small textures faster than one larger texture ( small ones too! ) but this is going to be videocard dependant, I'm sure.