Based on this post
http://www.m3post.com/forums/showthread.php?t=421385
It appears wheel manufacturers do shoot for a predetermined strength and then lighten as much as possible. So it seems like nobody really tries to max out on strength since they probably all shoot for the same load rating. Like others have said here, this means that the whole 8000 > 4000 argument really makes no sense unless you compare the entire manufacturing process.
This was a good discussion that for once didn't end up in a pissing match between certain groups supporting different manufacturers. Thanks everyone for keeping it a purely technical discussion.