I have a Monaro with 3.91 ratio in the arse end, its a much nicer alternative and makes better use of the 6 gears. A friend fitted a converter and a set of 3.73's on his <a href="http://www.ntsearch.com/search.php?q=auto&v=56">auto</a>, its also BLOWN - start saving for rear tyres is all i have to say !!
In my C5, the 3.73 with the auto is a good blend of highway manners and performance. 60 foots like a mother too, with the right converter. The higher numerically you go with the gears, the "tighter" the converter will feel if you run a big stall. I can still manage 26-27 MPG highway and RPMs are only a couple hundred above when I was running 3.42s. You'll love 3.73s, trust me