My experience using series 2 with the little wire antenna for this purpose has been 30 feet or one wall, whichever came first. I tried using an XBee in the middle as a relay, but couldn't get that to work. This was with the XBees set to 57K, I never tried any higher. On the other hand, I can send "hello world" from my recliner to the barn 150 feet away through three walls using the low power XBees....go figure.
I haven't pursued the idea further because it just hasn't risen high enough on my list. Maybe someday.