There are a few things here that sorta muddies the water. For someone who has both a geared bike and a SS bike, these will most likely be two different bikes. So when a rider switches from one to the other, he's not only switching drivetrain set up but also, frame, fork, wheels, riding position cockpit configuration, different tires etc. It'd be real difficult to keep track of which perceived differences(apart from lack of chain slap) that are coming from where.
Next is that us humans can be quite good at noticing relative differences, but quite sucky at absolute values. Something that'll turn out very minor in hard data can have a huge impact on the subjective experience.

And on top of that: since you have done your homework, you already know what to expect. That'll often turn into a self fulfilling prophecy. In formal testing, it's common to go to quite some lengths to prevent the test subject(s) from knowing what might happen.

An SS bike will certainly force the rider to vary his pedaling quite a bit more, and they're nicely forgiving under harsh riding conditions - if that's what you want.