Thanks @Gijs! Actually maxing out was not an issue. It was more of trying to remove the jaggies and flickers, like in Spa. Wanted to try CSAA but Maxwell no longer supports it so I was trying to play around w/ inspector.
First of all, there is no formal confirmation that the option to turn off HDR will be removed soon. That said, ISI have been advising everybody to turn HDR on for some time. It's because of what Gijs said, the textures on cars and tracks have been designed for HDR.
In HDR mode a texture is an "albedo map". There is a somewhat longer explanation on their website (http://rfactor.net/web/rf2/devscorner/texture-maps-and-color-saturation/) but the basic explanation is that the colors of the textures are interpreted differently. Put very simple, if you want something to turn up as white in HDR, you need to make it light grey, not white. If you make it white, it will become fluorescent.
If you turn off HDR, these textures will look "bland" as then they will look light grey.
The other way round, if you convert content from older games which do not have HDR, then the textures are way too bright, which causes them to all look fluorescent (or "candy like").
So, you can really only create a texture for either HDR or LDR (as non-HDR is called) and ISI has rightly decided to create them for HDR (and so have most modders that understand this issue). Therefore it is logical that at some point in the future, HDR will be always on.
Why isn't that the case already? Because initially HDR had a big negative impact on the framerate. That has now been fixed, the difference is small (but still there is some difference). So it's been left in for people that really really really need the extra framerate and don't care if the game looks bad. For the rest of us, HDR is the way to go!