The BFG are S rated in the UK 112mph, for that size; don't know if it's different across the world. There are plenty of MUD tyres that are Q rated at 99mph, but that wouldn't make any difference in many markets; as you can often fit specialist tyres with a lower speed rating than the vehicle, such as winter tyres; mud tyres etc.
Defenders(amongst others) with higher maximum speeds will happily run Q Mud tyres in many markets.
And again unbraked trailer size in Europe is always 750kg; although across the world this varies massively I guess, and of course, many markets have those electrical modules. The Grenadiers Gross Train weight is 7000kg's that's 3500kg vehicle + 3500kg towed (with brakes) which is pretty good by most standards I think,
State side the aftermarket people sell smaller brake kits to allow smaller than 20" wheel fittings to the more powerful Defenders, I believe.
Defender small brake kit takes the minium wheel size from 20" to 18" for a 400bhp defender.
So for now I'm sticking with my wheel size/Brake size theory (for now
![Thumbs up :thumbsup: 👍](https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f44d.png)
) as a main driver for the 99mph speed limit; which I agree is plenty fast enough.