Modern Vespa

Currently I'm using a very very noisy Suomy Jet.

Is there such a thing as a quiet 3/4 (open face) helmet at highway speeds?

I compared 3 recently at:
http://www.scooterdivas.com/forum/viewtopic.php?f=10&t=5016&sid=3fa1aee4650ba6d294d575ba3238eadf

And the quietest one I tested was the Shoei J-Wing
(the white one)

You could try ear plugs...use your discretion. Plugs will reduce decibel levels to a point where ambient noise can still be adequately heard (stuff you want to hear) while muffling out the wind noise.

Again, use your own discretion.

It is a mystery to me why more motorcyclists and scooterfolk don't use ear plugs more commonly. That way you can focus on helmet comfort, venting, whatever, and your noise is not an issue.

I think that Suomy Jet is one of the noisier 3/4 helmets
(based on reading a lot of user reviews)

I've been wearing ear plugs with my 3/4 helmets
and wonder if that would be enough with the Suomy

Those 3/4's do generally get very noisy once you're past 45 mph

Well I emailed Suomy to see if they offer a longer more covering visor...still waiting for a response.

May be a lot more than just the visor length. You need to consider overall design and effect of air flow/turbulance.

You may have to find a way to actually try one out or rely on reviews to find out what you find acceptable.

Note: Per previous post I use full face and still use ear plugs to minimize noise level.