I was recently behind a school bus going south to ft lauderdale and it was going 85. With School markings and all. They must inflate their tires right.
Shaun and I recently drafted a prison bus near Starke and it was hitting 90 at times.
For us bus converters its best to keep under 75 for the most part. But I like my shorties capable of merging and changing lanes at speed so 80 is a nice target to go for. Most of my cruising is 45-55.