Here are the three special weapon armed bikes, the Grav Guns on the Marines and a Combi-Grav for the Sergeant.
The Sergeant was made using a Ravenwing fairing, and Ravenwing legs, a MK VIII torso and a landspeeder pilot bare head. The aerial is from the Scout Bikes.
I think the Sergeant bikes with Fairings make them stand out from the rest of the squad members, deserving of his veteran status. I have a few other bikes on the production line, another couple of Grav Gun Squads and a few Characters, Libby, Chaplain and Captain/Chapter Master on a jet bike. With these characters, the squads can become Troop choices.
Cheers for dropping in, thanks for reading. See you at Warhammerfest if you are going!