I went through this same dilemma and ended up not doing any of it. I even thought about just pushrods or even just pushrods and springs etc. Pushrods seem like a decent idea, but the reason i didn't go with them was the though of adding the extra weight of the beefier pushrods which would in turn make it easier to float valves. How much easier? I'm not sure, I didn't do the math, but just the thought of it made me decide it wasn't worth it. The valve spring would just have to work that much harder to keep everything closed with more mass being flung around. Well, why not just add the springs? Well, I'm not sure how beefy these cams are, but back when I raced ATV's, stiffer valve springs and heavy pushrods on a stockish cam was a sure fire way to wear the cam out faster, for no reason. The extra spring pressure just puts more pressure on the cam lobes. It's not like I haven't seen a few 6.0 cam lobes wiped off on the forums.... so I also scratched that idea. I figured the only RIGHT way to do this was do the springs, the cam, and the pushrods all at once. I ended up not doing it simply because pulling the transmission to do the cam wasn't in the cards at the time. It also went from an original plan of $250 on pushrods to $1200-$1500 extra for the pushrods, cam, and valve springs and it just wasn't in the budget.
Most of my decision was based on theory and my limited budget, so take it FWIW.
