Just use Ravenslayer's grabviewport script (it's on my shader page) to grab at 5000px wide. Then you can get AA and high resolutions, which i think is the only reason you'd wanna render ?
Just adjusted a script that saves your viewport to an image I made it so that you can set a size upto 7000 in width and height and it will save your viewport out to an image I`ll probably adjust this one later on with some more options (maybe animation) http://leslievdb.dommel.be/Tools-GrabViewport.rar