OK... so let's get back to Explorers and forget the Mustangs (you wanted the comparison, anyway). The newer Exs appear to ride much smoother and are more comfortable than the older ones. However, they still retain good ground clearance and have, if ever so slightl, experienced the usual Ford 'bloat' regarding overall size.
During my usual duties, I do drive these fairly regularly (though most of my work is on SuperDuties) but I drive them on the street and don't usually find a need to push these things to their limits. Though the suspensions have become quite refined, they remain SUVs. As such, they are easier to force into delicate situations than cars. They are not "prone" to rollovers but neither should we fling them about the "twisty bits"... they are still SUVs and I can't make that any clearer.
Compare this to a gun.... guns do not kill people - it is the silly bugger hanging on to the gun that accomplishes that. Similarly, cars do not rollover though they do feature a group of controls that allows some silly bugger to command it to do so - some vehicles are a little more willing, but they still require sufficient driver input to achieve the undesired result. Often, in spite of the vehicle exhibiting obvious warnings of impending doom.
Bottom line.... Explorers can still rollover whenever we tell them to (most on the NG would be hard pressed to even infer that this is an indication of being 'prone' to rollover) - comparing them to cars is of little use (apples and oranges one might say). There is no finite answer to your question other than skid pad testing - and since these are not conducted in a real world setting (off camber corners, tar seams, road heaves etc. are not part of a skid pad) the information is of dubious value without taking other aspects of vehicle dynamics into consideration.
I've been driving 4X4s for something like 25 years..... some of them touted by the press as "rollovers waiting to happen". The few times I have approached being 'out of shape', I have found each and every one of these vehicles telling me that I best change my course of action lest I stop being a motorist and start being a statistic.
Finally, January will mark the 30th anniversary of my loving (and only) bride and I...... I fail to see the importance of this in this conversation but it does prove that some folks are very quick to jump to assumptions.
-- Jim Warman snipped-for-privacy@telusplanet.net