Not usually, but that does depend on the sub and how much bass a person wants. I think 100 is a bit high. though 100 to 80 isn't a huge deal.
True, the subwoofer in question does enter into it. Because if it produces enough acoustical energy high enough in frequency (mechanical noise, harmonic distortion, resonances, etc), it can easily become locatable. But yes, 100Hz is a bit high. I just picked it for an example.
But furthermore, as I brought up, room interaction comes into play at those frequencies. So by using a low crossover frequency, it becomes difficult to guarantee that the left and right channels will producing similarly good mid-bass with respect to each other.
On a somewhat related topic, I have heard of studies on the topic of channel separation at very low frequencies; stereo bass and it's effect on the spatial aspects of the listening experience. The conclusion that can be drawn from the studies, and from external commentary, is that below 70-80Hz, there is no audible benefit to stereo bass.
but I prefer a 6.5" driver in many cases over a 5.25"
As it often pertains to bass response, I would prefer a larger driver for low frequency too, but it is very important to consider the whole of the spectrum that the speaker is reproducing, and driver size alone provides only a basic hint of the audible characteristics.
