Those three states use 109 megs with City Select v7 - way beyond the memory of the standard Vista C. We are using a Legend C with this software and so far we haven't had any issues having the areas we live/work/play in. We have Atlanta and most of north and central GA loaded on it.
As for loading maps, Mapsource is very painless. Select the areas you want to have on the GPS and load them - very easy. The program also tells you how many megs your selected map segments are. For us, we obviously have to keep it at/below the 24 limit.
If you stay around in one area most of the time, the base units should be fine. If, however, you intend to go touring through numerous states then the expanded memory may be what you need.
We bought our Legend C 2 days before I learned about the x series, and after a long debate decided that the standard unit was more than adequate for our needs. Most of our daily travels are well within the map area loaded on the GPS. I admit, however, that the idea of more memory would be wonderful if/when we take an out of state road trip.
If you do decide on the non-x unit, make sure you get City Select (not City Navigator). The map segments in Select are much smaller and better suited for the limited memory.
Hope this helps!
Dos Gatos Diablos