Overall width is very different from the width at the roof.
The 48" would fit nicely, similar to the factory x-bars. Probably blend away visually. the 58" would extend out just a little. It would probably come to the tops of the doors. I think anything wider would start to look funny...?
I went with whatever width the Yakima Fit Guide suggested...58", I think. Looks fine to me, don't think I'd want anything wider. I'm not sure 48" bars would even be long enough to work with the Lowrider mounts.
Depending on how DIY you are, you might consider upping the size on the fairing, but you'll need to do some customized notching to fit around the side rails. I went with the recommended fairing widtha and it drops down in between the rails, leaving a couple of inches of crossbar exposed on both sides of the Lowrider mount. At least psychologically, I felt this contributed to wind noise...don't even think of running without a fairing. I found it bothersome enough, that I enventually removed the rack except when I need it.
Rackless...I removed the OEM crossbars too...does emasculate the Beast just a bit...maybe I'll have to reinstall them now that I'm thinking about it.
It really depends on how much stuff you want to put on the roof. I"ve had as many as 4 bike mounts on a set of 48" bars to give you a point of reference. Legally, you can go as wide as the side view mirrors which is good for carrying a canoe plus other accessories or 2 canoes. Narrower bars will be quieter to a degree but there will always be more noise than with just the factory rack. If you do go with bars that overhang the roof by a bit, I'd recommend padding the ends with tennis and/or racquet balls. I walked into a load bar in a parking lot a while back and it leaves quite a bit to be desired.