I'm the sort that loves lots of headroom and therefore always buy the biggest I can get. 2000 watts is nothing to me (I have two amps that are that big). However, in the amp world, I find that amps have a sweet spot where they make their best tone. That's very seldom in the lower end of their power output capability. That's what I was saying when I said the 500 combo is not an ideal bedroom amp - when you get it into it's sweet spot where it sounds killer, it's blowing the windows out. It sounds awesome, but just louder than Hades. I suspect that the Rumble 100's and 200's are the same, in that they have a sweet spot, because I think they have the same front end as the 500. But because of their lower wattage, the SPL will be a lot quieter. Don't get me wrong, I use my 500 combo as my practice amp daily and never think about getting rid of it. But I am often one loud mofo.
As for your bike analogy - I don't do bikes, but cars. Back in the day, my Z28 wanted to cruise at 80-85 mph. It was smooth as silk there, felt awesome, and any slower just felt like i was working to hold her back. The cruising sweet spot. Several tickets later... So it's really the same thing, IME; machines have a sweet spot at which they seem to like to operate. Even my Dremel likes a certain speed, a little over halfway just gets the work done cleaner and faster. Go figure.
Excellent points, bdplaid. It is true that amps (and other things) have their sweet spot. Tube amps are the best example of that but even the solid state amps show this. But I loved the tone of the 500 even at crazy-quiet levels.