Superior Axle does have two versions of chromoly axle shafts, the Discovery Series and the Evolution Series. The Discovery Series is their overseas model which is probably closer to 4140 than 4340, understand that it’s not a 'quality of steel' issue but a 'difference in standards', there is no true "4340" used overseas. They call it something different and it’s close; but, not exactly the same. The Evolution Series is what we’re after, the good stuff, strong beefy home bred axle shafts made right here in L.A. Superior’s Evolution Series chromoly axle shafts are made right here in the USA.
Basically, what this all equates to is you taking a minute to ask yourself, if you would rather save a few bucks, possibly break a shaft leaving you stranded somewhere and resorting to that awesome "no questions asked warranty" or, would you rather pay the extra money to help keeping it from breaking in the first place? It really is amazing how few Evolution series axle shafts superior has to warranty out every year....the number lingers around 0.