I sympathise, I spent a couple of hours in a store in Kircaldy trying on all of their helmets a couple of years ago....bought the one with the best fit and construction, ended up with a Shuberth S1, £400-odds. My wife was with me and insisted I get the one that was comfiest regardless of price. Its a double D ring fastener too, I hate the ratchets/buckles & can't understand why they fit them, they must be more expensive than a simple d-ring!
Having now got one, I too couldn't go without the sun visor - its ace.
You spoke about the curved bottom to the visor - Shuberth let you take out the sun visor and re-insert it upside down if you prefer a straight edge, so you can set it up the way you prefer.
Saw some decent priced Uvex helmets at
http://www.louis.de but no recent sharp ratings...
Good luck in your search (was going to say quest...

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