It's true that some brands will fit your head better than others and you may find that different brands require different sizes for you. You should try some on.
That's one reason I've stuck with Shoei over the years. They always fit right and I know what size to get, making an online purchase possible.
For what it's worth, a solid color Shoei RF-1100 can be had online for as little as $400 including shipping.
One other consideration, just to make your choice a little harder (!), is if you would like a Pinlock visor. It is a fog-resistant visor that employs a double shield, like an insulated double-pane window. They only have visors for certain helmet models. I'd love to have one because I spend so much time riding in chilly to cold weather and have to ride with my visor open a bit.
The Pinlock fog resistant system is made up of two elements - a Pinlock ready shield and a Pinlock lens. The Pinlock is a very flexible system, allowing you to switch the color of your lens adjusting to changing weather conditions. You can click one lens out and put the next one in. Make your choice.