yeah they're right. It all depends on where you're cruising. Between stoplights in town, I just go whatever'll get me there when the light turns green, 3 to 4k. If it's gonna be a long time, I slow down way back, and split lanes to the front, hopefully getting there at the right time.
However, on the high speed part of my frequent commutes, I go 6k to 7k for a few miles- (and that is definitely the best part) so it all depends.