Have done a lot of Internet reading about rods today....... Conclusion: both I beam and H beam rods are run in ultra high output stuff. Different manufacturers carry one or the other or both .
Going BACK again to MY initial comment, the Scat 4340 I beam is a better rod than the 5140 Eagle SIR rod.
The Scats are in the motor I am installing and shouldn't be a factor at the power level I will make. If I thought they were I wouldn't have bought the motor.
I ran Eagle H beams( 4340) arrow billet rods, and compstars in previous engines.... All made more power.
Is a Scat I beam a trick rod.... No... But it's not because of its I beam design.
Manley's top shelf stuff is I beam
The Scat rods with an ultralight spinning assy at 6500rpm and at or under 500 horse should be fine