For those of you that carry kayak(s) on top, what do you use?

I'm thinking about switching out my 48" crossbars for some 58" so I can have 2 kayaks side-by-side... but I also noticed that yakima sells the stacker/bigstack which lets you fit up to 4 on their sides.

I need to be able to carry 2 kayaks... any suggestions/experience?