"The Chart" used to be on M4Carbine.net, but was removed because a particular manufacturer used it to promote their product.
Honestly, it all depends on what you want an AR to do. If you want ultimate reliability on a DI gun, then the chart is quite useful. If you want a varmint rifle, then it's pretty useless. I have a friend who built a 1/2moa varmint rig from a Model 1 parts kit. His runs great when it's clean and will out-shoot my Colt all day long. But I can clean mine with sand and lube it with pig blood and it'll still shoot. If his gets a spec of dirt near it, it quits. When I look for one, I look at the fit, proper staking, good barrel, and good bcg. Read a lot and educate yourself.