JMHO, go with the cast iron...

I have my Lyman mounted on a true 2X8 right know. Before I started bolting it down I did c-clamp it down, so that has worked for me!

You are going to laugh at this, room is tight for me right know and I mounted my press on an old iron fish tank stand. lol. also, look at Lee's websight, they have a roomsaver bench for a press.