I'll go out on a limb here but there is a pretty big difference between downhill skateboarders and your typical longboarder. Longboarders are mongo pushing, sandal wearing hippies/dweebs that walk or transport themselves from class to smoke shop etc. Downhill skateboarders on the other hand are gnarly and they bomb alpine roads up to 50-60mph and power slide on gummy soft wheels to slow down (meanwhile leaving 20ft+ shredded urethane marks in their wake). I don't understand the disrespect towards downhillers, inverted kingpin or not. They are A-OK in my book. I would absolutely love to make the mary hill journey one day.
Living in the east bay, I've always loved bombing hills and about ~ 7 years ago setup a dedicated downhill complete for mountain roads to bring on camping trips. Its a skaterbuilt slalom board, 9x33, multi drilled and i have it set to the shortest 17" wb with Indy 129's and blood orange 72mm/82A wheels with swiss bearings. Its fast as fuck. According to my old GPS app on my iPhone a few years back, I got up to 36mph in Lassen County on a family vacation on a mild grade road for about 5 minutes straight. Its exhilarating. Those wheels maintain the roll speed and Its like driving a cadillac. Smooth and silent. Pretty sure I've exceeded that speed on shorter/steeper hills but don't have the gps data to confirm.
In regards to slowing down from those speeds - On my normal street setup, I can powerslide and bluntslide/noseblunt slide ledges but definitely NOT on those soft downhill wheels, they're a totally different animal. At my age I have no interest in mastering downhill power sliding and dealing with the 20mph+ slams and road-rashes in the process (I like my skin intact). Instead, when the opportunity presents itself, I scope out the roads, drive up and down and find a section that naturally ends where I can progressively slow down to the flats. Ive tested a true downhill board with a ~20ish+ wheelbase but I just couldn't adapt and went back the skaterbuilt as its a nice compromise. If you made it this far in my wall of text, godspeed.