The rack will hold more than 5 lbs. Suzuki puts that out there as a CYA type of thing. I have the Saddleman X-large touring t-bag that I know for a fact was at least 20 lbs full and packed and it held it just fine. Of course I wasn't riding rough terrain and no huge bumps to contend with either.
I myself was concerned about the 5lb limit but with the bag I have it seems to be working. I would rather have one that goes down to the fender for added bracing and all that I have seen that does that will not work with the factory backrest.
I did come across a used Suzuki billet rack just like the one I have that I am going to check into having some extra bracing modified to it and then re-plated once I get done.
I would say though if you go with the factory billet rack then you can pack an easy 15 lbs on there and really more but that is your call.
__________________ Biketoberfest 2006 flashback courtesy of Intimid8er: "Like you knew damn well you shouldn't eat something like that, but all be damned to hell, you were gonna eat it!" 
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