I'm seriously considering the 54 SD for my secondary mower for my business, they have a couple at the dealer I've been looking at but I have some concerns about the FR Kawasaki for the business to whether it would hold up or its longevity.
Seems like with your satisfaction with your Grandstand you would consider a Toro Titan(especially the MX series). IMHO, a hands-down better ZTR that the Hustler Raptor SD or it's predecessor the Sport and would make a great addition to your fleet(and you know that Toro has one of the best warranties in the business).
Your right, though, I would worry about the FR series holding up under commercial use(the Toro website isn't specific, but it seems to me that the Titan MX comes with the FS...Heavy Duty....Kawasaki).
P.S.
The 54" doesn't have an engine guard/shroud...only the 60". I find that a bit chinch on Hustler's part(you definitely would have to purchase the guard "option" for mowing commercially. Also, the plastic spindle pulley covers are a real turnoff(for me:0)
I seem to remember getting advice when I was looking to avoid those(Bad Boy also has plastic.....another reason I didn't get that Outlaw, thank goodness:0)