The G614 RST is rated at 75 mph because its a LT tire. Many mistakengly see the RST and may think its some how a ST tire. Its not...
Goodyear says the RST stands for "Regional Service Trailer" and is targeted at regional service haulers.
As other better informed members have said we have several brands of ST tires that carry a speed rating higher than 65 mph. I would be looking at those brands....if I was confined to a ST tire.