I have had an Arai RX-7 for about two years now. First thing first, it is a very expensive helmet, but I feel it is money well spent. The venting is second to none, seems like it even moves air at a standstill. Very comfortable and the build quality is obviously excellent.
On the down side, it is a bit noisy and the visor does fog on cold days, but only at a stop. Once you get moving again, the airflow takes care of the fog quickly. But the fogging is very annoying and obviously unsafe. We can land a rover on mars, you think we could come up with a visor that does not fog.