cal-tracs question

Well, I don't have the money for their mono leafs. And my stock springs are shot. I wanted to go with JC whitney springs because I've heard good things about them plus they're only $60 each!! I'm just wondering If i should go with the heavy duty 5 leaf or the stock replacement 4 leaf. Any thoughts?? I was leaning towards the 5 leaf just because they will probably last longer and will take longer to sag after all the abuse I plan on putting them through.
Cheers!

here's the link

Spring link