The reports coming back from the skippers and crew regarding cruising in "sub-optimal" conditions are fascinating. Over the past few years I've done more than my share of this stuff and I had no information like this to prepare me. Fairly much without exception, I have ended up by trial and error coming to the same conclusions that you guys listed:
Dry suits good, everything else a waste of time
Gecko helmets good - need intercom patched into VHF + full visor.
Wear everything you will need, including food and drink.
Arsing about with electronics is difficult - be prepared to use the compass for long sections/periods, it's much easier.
Good handholds are essential - most leisure RIBs are badly served in this area.
You can't see through a wet screen AND a wet gecko.
You'll be driving while standing
Gloves are for girls and passengers.
If you can see the RIB ahead of you all the time, the swell is less than 3m