Once you get up into the +$500 range of receivers, you're pretty much always going to get good sound quality. What you'll get more of as you go up the price scale is power & features.
I just read a post from Midcow2 that mentioned a SPL calculator
here.
As I recall, the THX spec is to be able to produce 105 db. To get 105 db, at a 10' distance from my very efficient speakers (96 db) takes about 40 watts. To get the same SPL from the Sierra-1's (87 db), you're looking at 300 watts - per channel.
On the other hand, 100 watts / ch (real watts, not advertised watts) will get you up to 100 db, which is still pretty loud. I think I'd lean towards features, as long as they include pre-outs. Add an external amp later, if you need it. Could well be that you'll find you don't.