Frank,
i feel that I boxed myself in a little sticking with cast, so it will limit my cam selections if i want to upgrade from my stage 2 Schneider cam. With that said, I might contact the more L-6 engine friendly builders to profile my next cam to take full advantage of the cast limitations. I have a read many posts declaring 7k to be the limit, and I would want a cam that started tapering off right at that limit.
You will be pleasantly suprised of the torque of the little ole L24, especially if you take full advantage of it's power-even at the cast limits. I guess it depends on how deep your pockets are and whether you have to have new pistons or not.
The only plus for me with having cast is if I decide to pressurize, the cast will probably be a better choice.
Don't forget to notch those bores!!