Mark,
That is an interesting point about too much suction. I was shopping for one not all that long ago and probably will be again someday. But what I ended up with for the time being is a small 6 gallon ShopVac Quiet Series. I will likely be posting a picture tonight as an accessory for it was delivered today (the rigid flex tube and attachment). I have a CleanStream HEPA filter in it and I daisy chain through a chip separator. I admit that a big motivator for me was that it was cheap, but it is just as quiet. The sound dampening isn't as good, but it has less power and therefore less sound to dampen. People in the next room watching TV don't notice when I have it on. It has the large size inlet, but the standard hose that came with it is the smaller size with an adapter which usually works better with a sander. I have hoses of both sizes as I have another powerful wake-the-dead loud old ShopVac also. Anyway, when I got mine they were about $35 at Big Lots, supposedly for factory reconditioned, but mine was a new one mixed in (I did not complain about that mistake) so I have a full warranty and everything. It was a no brainer at that price, but even at whatever normal is, it is probably worth considering since you said it is just for the sander.