I was looking at:
http://www.spidertrax.com/Ultimate-300M-Axle-Shafts
We start with only the finest US grade 300M (used for the axle shafts) and aerospace grade E4340 (used for the yokes) billet chromoly
It just seemed that there was a reason for their assertion and I could not place my finger on why.
The reason why I was looking is Oliver rods uses E4340, Dyer rods use forged 300M, Cosworth uses 4340,
Pauter uses billet E4340 or
titanium, while
R&R Racing Products and
Saenz Performance puts the options out for the customer to decide.
Manley uses 4340 in their "lightweight" rods and 300M in their dirt series. To top it off, Carrillo uses Carrilloloy (a proprietary blend of steel).
In terms of a connecting rod, it looks like 300M > E4340. Can anyone confirm?