There's a 5400x2700 version. The best you'll get with that is 4096x2048 (for a texture size anyway - you'll likely need to split it into pieces if you were to use it. PNG preserves the exact colors. I'd recommend downloading the 5400x2700 image for your game then resizing it to 4096x2048 and splitting that up into 8 1024x1024's to use as textures.