The major "floaty" feeling from the rear at speed can be caused by weak springs, and the soft rear ARB.
Opposite lock went in my car, and I'm sure will tell you it was 100% stable even well over 100, on a private road, this stability cam about due to the 22mm rear arb, I used the car for 1 month each with 16mm arb, then 18mm arb, then 22mm adjustable arb on mid setting, at which it is the same as a escos one, the high speed stability was awsome, long sweeping bends on private roads at 150 no problem, 10,000% more stable, not found a downside yet despite what everyone told me, I do have coilys and run 200lb on the rear.
tabetha