I believe one reason why you do not see t-tops and targas on SUVs (well, vehicles with that full cab and rear space), is because at higher speeds, that rear will become such an intense vacuum that passengers in the rear, and eventually the front as speed increases, will be enveloped into an intense "walloping" sound. Many may get that with just having a removable or retractable sunroof, but it wouldnt be as bad as an actual removable cab roof space. I installed an oversized sunroof on my Amigo some years back and I couldnt take out the sunroof unless the rear soft top was removed. That vacuum and compression in the rear got so bad at higher speeds that the soft top was actually tearing at the connection pins. It basically acted as an umbrella or a parachute. I think auto designers keep this in mind when creating SUVs cause even with no removable rear like the AMigo, that vaccuum/compression still exists. I don't how this may affect your driving performance or car stability, but I know that having that sound of air concussion blown into your ears 5 times a second sucked, heh.