Just 'cause your tires are rated at a higher max that you would really go, doesnt mean you must go that fast.. The higher rating means that you have more headroom for load rating and heat generated which makes for a safer tire and less chance for a blowout at speed.
For example, passenger car tires are rated at above 100mph, but that doesnt mean you must drive 100mph
This is also why LT tires on a trailer are usually better than ST tires. ST tires, since they arent meant to carry live people, are rated much closer to the max the tire will actually handle, especially at speed. Being able to handle 3500lbs at 65mph is actually much weaker than being able to carry 2000lbs at 100mph.
This is also the reason Regional truck tires are cheaper than Long Haul/OTR tires.. The Long Haul tires are rated to handle the load for thousands of miles at (usually) a higher speed and with more heat buildup, while the Regionals are not as they are meant for short distances and have a much higher chance to blow due to speed and heat when used in a Long Haul capacity.