I have had new E rated ST Maxxis tires blow out in less than a year with less than 3000 miles on them. When crossing the desert in summer ST tires blow out due to heat, LT tires do not. It took me a while to figure this out but LT tires are designed to deal with heat and ST tires are not. Maybe where the temps are lower in summer a ST tire will last for years but when the pavement is so hot the asphalt is melting they blow out fast.
SO to answer the question I am comfortable with LT tires for as long as it takes for them to get cuts, cracks, or worn. I watch for center tread bulges, uneven wear, etc. and in 3yrs have not noticed anything that indicates tread separation/over heating. I am still on my first set and they have already lasted longer than any ST tire I ever owned.