The need to be able to put at least the balls of your both feet down is important when pulling up to traffic lights where lorries have worn two shallow grooves in the road. If you are already on tip-toe, the extra distance to the ground can mean the bike leans over beyond the angle where the weight (215kg!) becomes unmanageable and leads to a stationary dropping of the bike.
I'd always lower the bike rather than the seat as less padding (for my bony arse) will affect comfort. (Anyone tested a supposedly 'comfy' Tiger 800?)
To answer the original post, on the motorway the Wee/Glee is absolutely fine and will sit very happily at 90mph, and even though it will go well beyond that, anything above 100 (on the speedo) works the engine harder than I want to. (Of course, the added benefit of this is that at less than 100, you're probably going to get a ticket. Over a ton and you'll be facing court and a ban).
I sit my Glee at 80 -85 (on the speedo, not a real 80 - 85) and get 60mpg.
I've been riding for 30 years, and think the Glee is an astonishing bike for the money. Great fun to ride, lots of useful torque. Cheap to insure. Coming from a 1000 Varadero, the only thing I find is that A-road overtakes need careful planning and execution, as if the car you're passing decides to accelerate to make your life difficult, there's not a huge amount of extra zip on tap. Just keep on top of the cleaning and GT85 for the fasteners or watch it rot before your very eyes. My just-bought 8 month old one belonged to someone who I suspect was quite lazy at cleaning it as it is already corroding, and I'm having to work hard to bring the finish back.