Now admittedly I don't know you from Adam, but I'm having a hard time imagining any "needs" that would require driving a beast like the one in question at 75 mph in any kind of crosswinds that would be an issue. High cog, heavy weight, and 38"+ tires don't generally lend themselves very well to high speed driving, unless you never intend to turn the wheel.
That's not to say it can't be done, but from a safety standpoint it's not all that advisable. Any kind of emergency manuever, like avoiding the texting teen in front of you that just went tires up because he/she forgot to look back at the road after sending a msg to their bestie, would be an iffy proposition at best in any rig of those proportions.
I guess to finish making a short story long, from my experience (and looking at the rig in question), I would imagine it's about as stable as you can get considering what it is, but as far as any highway speed emergency manuevering goes... well, you rolls the dice n you takes your chances.
