yes in my own car with a friend, left 5:30 am and made one short stop at a petrol station on the way, took about 5 hours from where I which is just a little south east of BKK.
Its an impressive modern racetrack by Thai standards, the only thing which would make it better is some elevation, (like Bira, or my favorite UK track Brands Hatch) but the land it was built on is totally flat so that was not possible.
Would like to go to a car meeting there also in the future.
I guess it's not too bad then, 5hrs is still at the edge of acceptable.
I can foresee a couple of PTT stops for Amazon iced coffee along the way when I head there in the near future
It is completely flat as seen on on board videos,
as for circuit elevation, it does get easier if the land had natural contours but I don't think man-making a couple of track sections with some banking or elevation would have hurt the Buriram owners much, nevertheless, it still look like a glorious circuit to drive on, reminds me a little of Yas Marina, which is almost completely flat as well, but nothing as wide as Buriram