I like anything above stall speed plus 10 knots, being in the air is what counts.
But if doing the big circuit of Oz, speed on a tank full does reduce fatigue and is better on the bladder. It is a long way and extra distance per hour is your friend.
I always like a bit of grunt and range in reserve for comfort. 30 plus years of motorbikes has taught me that. A bit like touring on a 250 compared to a BMW flat twin, both fun but one is much more relaxed to really enjoy the trip, at any speed.
Mind you I am happy to have a postie bike with wings.