I reverted back to Buffalo firmware from DD-WRT because the current version of DD-WRT will not connect and stay connected at 300Mbps. Buffalo firmware has much better wireless performance (at the moment).
To revert back, just do the following:
1) Download the file wzrg300nh_original.bin from here: http://www.dd-wrt.com/phpBB2/download.php?id=13418 (This file is Buffalo firmware v1.65, but it is stored on the DD-WRT website. You must register with DD-WRT to access it).
2) Use the firmware update feature inside the DD-WRT webGUI to install the above file.
3) Make sure you wait until the firmware install finishes completely before you reboot the router. (Somewhere around 6 minutes, but wait longer if you aren't sure.)
4) Be aware that the router's IP address possibly changed. (Depending on what address you had set it to.)
5) Configure the Buffalo firmware to the way you want it.
6) Download the latest Buffalo firmware and use the Buffalo webGUI to install. (Tftp is not required for any step.)
Keep the wzrg300nh_original.bin file in case you want to try the DD-WRT firmware again after they get the bugs out.
If you have "bricked" your router and want to revert back to Buffalo firmware, follow the procedure given at this site:
http://www.dd-wrt.com/phpBB2/viewtopic.php?t=72544
Follow the instructions given by flytiger and LOM.
You still need to download wzrg300nh_original.bin, but you will do it by TFTP.