My wife and me travelled for one year using the eurocom model from www.autocom.co.uk.
Don't know if this model is still available, but the products from them are very good.
On the Tiger, we could keep a conversation up to about 120 km/h, on the average. But how well you hear each other depends not only on the quality of the intercom, but also on the turbulence on your bike (plus your helmet's noise reduction abilities, current wind direction and speed, etc). You also have to fine tune the location of speakers and microphone. It took us a while to get use to, but when we did it was worth its weight in gold, and after about 70-80 Kkm the system still works.
Be careful to avoid to much humidity entering the system and try to keep the protection on the mikes as undamaged as possible. We had some static noise problems when riding in very wet weather over longer periods.
And finally; Don't by the cheap models that flood the market. They're a waste of money.