Z-wave range


I'm considering setting up a z-wave network, but I want to start off with a few devices and then grow it from there. Is this even practical given that the number of devices is a major factor in the range and reliability of the network? Can anyone using z-wave give me an idea of the maximum safe distance between devices? Thanks.
This varies from install to install but my first Z-Wave device is about 30 feet from my Z-Wave controller. The others are all within 15-20 feet.
I got bored when my mother in law came to visit last halloween and tried a few outdoor tests on zwave.

I went across the street with my Intermatic master controller and a measuring wheel. From across the street (82ft) it worked perfect. I then went another 58feet still worked perfect. Went another 66 feet and it was very inconsistent.

Test number 2. I took an extension cord and module out to the drive way. I had to guess which module was sending the signal out to the drive way but the closest 2 where about 45 feet away. I moved it another 12ft with the same results. Another 12ft and it wouldn't work at all. There's a lot more things to get in the way inside of coarse. Not scientific but still interesting. Take it for what its worth.
It's very environment specific given that there's no such thing as a dedicated "repeater" that you can hardwire back to a master controller - the devices themselves do the repeat function.

I currently have about 13 devices mounted, with another 12 waiting. On the flip side of the above experience, I have a very punishing environment in my 96yr old house. Not only is it a plaster/lathe house, but it's been extended 3x so there's several inside walls that used to be exterior walls, meaning insulation/lots of wood/etc inside. And then there's the fact that I have more wireless pollution than you can imagine: In my neighborhood, houses are about 15' apart. I have multiple baby monitors, microwaves, 802.11b/g on various channels, 900/2.8/5.6GHz cellphones, power lines above, bluetooth, etc etc etc.

If I were to "just" use the controller or the ThinkEssentials software, I have problems with the lights on the other side of the house, about 60' away, even though i've got a few switches in between. I had to make sure I had switches every 10', and Dean had to upgrade the zWave CQC driver so that it was a little more patient and would retry sending commands.