Hi from a happy owner of a 2013 7.5 FX. I ride mostly on the paved roads (streets and paved trails), though some of the roads on my regular routes are pretty crappy (i.e. tree roots, potholes and cracks). My 7.5 FX can handle them pretty well. I had a 8.4 DS for a very short period of time, thinking it was the right bike for the kind of rides I do. As it turned out, the carbon fork on the FX is enough. I compared the two bikes on the same bad roads. Even with the suspension unlocked, the 8.4 DS wasn't all that much smoother than the FX. And yes, the 7.5 FX is definitely lighter than the 8.4 DS. The 7.4 FX Disc would be a bit heavier due to the disc brakes and fatter tyres, but it should still be a great option for you. Good luck!