At least with the Sirrus, the geometries should be the same as the other Sirrus models so you should still try to ride one to check the fit (I imagine they most have at least one Sirrus model!). Not sure if the same holds true for the Treks. I couldn't find a weight for the FX 7.5 but I found a bike shop that claims the Sirrus Comp weighs 22.92 lbs (
http://www.edinburghbicycle.com/prod...sirrus-comp-12) - of course I imagine that also depends on the size of the frame to a slight degree.