When I did the French road rallye last month with Southern Kit Car Club I noticed that a number of cars were fitted with intercoms. Certainly made communication between driver and navigator that bit easier.
Anyway, I've bought myself the Terratrip Clubman intercom and the Clubman Practice Headsets. I tested them last week on an 80 mile run. Overall, I'm very pleased and would recommend the set up. You still get just the right amount of ambient/road/exhaust/engine noise without being deafened.
Stationary and at speeds up to about 40mph conversation is perfectly audible. From 40 to 60 the wind noise becomes noticeable and then as you get higher speed it does get quite noisy, but usually at this point you are only on a quick straight before slowing again.
You can also run the GPS (phone in my case) into the intercom unit. This is really designed to take an input from a two-way radio. It does not work so well with my phone as the output signal is too low and/or there is an impedance mismatch between the units (phone is too quiet compared to the other persons headset). I've ordered a small headphone amplifier unit to see if this helps.
On last week's run, with a beanie hat, Dixon goggles and practice headset on both driver and passenger were very comfortable. I think it does reduce the fatigue a bit too. I've no windscreen or aeroscreen at this stage. There is some slight alternator noise at low speed and occasional breakthrough from the phone signal.
Depending upon your taste they look quite business-like to, whether on the head or hooked over the rollbar.
Next I'll invest in the full face helmet version as an option for track/motorway use.
It wasn't in the instructions, but I believe an essential part of the operating procedure is to remove them when in tunnels!