Welcome to AT Network Forum.
The default of the Linksys is about 40mW.
In theory, you can go up to 251mw.
However since the Router was Not design to High output when you increase the output you increase the Signal and the Internal Noise as well. Signal to Noise Ratio (SNR) is more important for good Wireless performance than pure power, so increasing the Linksys power at will does not necessarily provide better performance.
I use a WRT54, I raised the output few mW at the time while testing distance and measuring SNR my unit balance point was at about 70mW. After few weeks of use it got noisy (probably due to the extra current and heat on the internal components) and I had to reduce the output and currently it works well at 53mW. Reports of others indicates that 50 ? 60mW is the common balance point.
I have a Buffalo too (the regular unit) at the default ~40mW it performing very similar to the Over Powered Linksys.
My guess would be that the 80mW Buffalo would do much better since it is designed for this output.
Some people on this forum use Cisco 100mW and they very pleased with it.
:sun: