Think of it in terms of megapixels. The limit is the amount of video memory the card has. If your target users have a 32 MB video card, an 8 megapixel bitmap is the largest you can go (except if alpha was used). 512x512 is 1/4 of a megapixel or 256 kilopixels (in relation to bits and bytes, though it'd technically be 262 KP). 32x2048 is 64 KP. 512x512 would allow for higher resolution, but for the same KP value, a 256x256 would also work. I have used a 16x1024 texture once (for a sky with basic fading) and didn't have trouble. 32x2048 should certainly work, unless the user had a 128 KB video card (such things are ancient nowadays).