The RD-X is a different material and probably more positive than my MD-X, which is machined aluminum and weighs a ton. When I use the std. port with 60mm, the housing is very negative, to the point that I sometimes get shoulder cramps after a full day of diving it. OTOH, when I put the 8" fisheye dome on with the 10-17, it is so positive that the dome flips upward if I let go and I wear 2lbs. of extra weight to keep from floating off of my safety stop. Best thing is put the whole rig together, float it in the tub or pool and adjust the buoyancy characteristics for each set-up. Right now, I'm looking into tape-a-weights (wheel weights for cars and motorcycles) to put on the dome shade to make the rig neutral underwater. I might try a PVC pipe float between my strobe arms for the macro port as well as I get tired of lifting weights underwater. I can't comment on various ball end strobe arms, as I've only used them on an adapter for the strobe end of my loc-line strobe arms.
