A Sirrus with stock tires would probably not be happy. I have 32c's with knobbys on mine and it does okay on crushed limestone and dirt rodes. Crushed stone (some people refer to it as gravel) or things which require suspension are more difficult.
Either bike can probably cover what you are looking for, but the Sirrus is definitely road oriented. Know nothing about Trek 7.3, or any Trek for that matter, but many many folks ride them.
Last edited by RollCNY; 08-11-11 at 06:32 PM.