Just drove 400 kms yesterday, with five hours off road. Its kinda wierd having 20 forward gears to choose from!!! All said, mileage was about 15% better. Used the OD all the time, even when in low range off road. Had to tow an older Series IIA about 15 Kms. Used low range as it died on a long hill on the highway. Pulled it in low range and shifted to OD once underway, it was very smooth and quite good.
As for noise reduction, never had to touch the stereo to increase the volume, not once. Cruises at 140 Kph no problems with the stereo playing and the converstaion is normal. Have to down hsift into fourth to overtake but that means going 150-160.... still not an issue. Without the OD the 1:4 t-case was very loud at these speeds. It'll cruise all day long at 110-120.
One of the best mods I've done. Now I have a spare LT230 1:2 that I didn't use when I decided to go this route. (Will get rid of that soon, when I clear out the garage). FWIW the 1:2 T-case has a reduction of 15% and the Roamerdrive 28%. My Td5 pulls like a train with the OD engaged from 1st gear. Thought about this for a long time and decided to chat with Ray Wood (the inventor) and it sealed it. Give him a call or email him in North Vancouver.
Hope this helps some. Feel free to ask more questions, happy to help out.
Cheers