My $0.02
X10 uses combinations of PLC and RF for appliance/light control remote control.
In an "unhindered environment" (which in reality does not exist) and with proper phase coupling the PLC signal will, in theory, propagate through all electrical branches in an average sized home and will make it to the utility pole transformer. At least that's the way everything worked back in the 1980's.
Today however that ideal environment does not exist. So much electronics in the home now utilize switching power supplies (including CFL bulbs) which generate tons of electrical noise coupled back on the homes power lines. This noise can corrupt the X10 signal. Also switching power supplies and UPS's have built in filters which many times, acts as a "signal sucker", attenuating the X10 signal. Finally, the originating X10 signal is only coupled to one phase of the US homes internal wiring, so must somehow get coupled over to the opposite phase. Again back in the 1980's and 1990's the homes 220V appliances helped to perform this task since they bridged both phases. Today, some type of passive or amplifying coupling is almost always needed between the phases to ensure the X10 signal gets from one phase to the other.
These caveats are one of the main reasons you won't see "typical" propagation figures.
However there is a forum comment from a user who is pushing PLC down a 250 foot run of Romex to an out building. I am sure he had a repeater/coupler in his system.
Now about the RF range...sigh, again there is no "unhindered environment". If you search "range" on this forum, you will see it runs from 10 feet to 100 feet depending on open air, number of walls, construction material, antenna modifications...etc.
Finally I think you will find this series of PLC articles from "Uncle Phil" very informative. There will be a pop quiz next Thursday.
http://www.act-remote.com/PCC/uncle.htm