So, I've mentioned the E6 idea before.
For those of you not in the know, E6 is "the game inside 3.5". Players can advance to levels 6, and after that, gain feats instead of further levels.
It keeps casters toned down, lets martial characters shine, and generally keeps the game at a sweet spot where everyone can contribute without the need for ridiculous amounts of magic gear and optimisation.
It removes some of the "zero to hero" charm of D&D, but it also brings forth the gritty nature of the lower levels. There's little in the way of resurrection, or city-levelling spells, or even planar travel. Things are just... Lower scale.
And as such, you can't just throw an E6 game into any old setting. Many have high-level NPCs running around, well-developed cosmologies that you can visit, and scads of ridiculously overpowered villains hovering around. Eberron is probably the closest match for E6, although Ravenloft would work really well too. Planescape... Maybe. It would take a lot of weird jumps and fits to manage it, but hey - that's Planescape in a nutshell, really.
The Forgotten Realms is right out.
So, in my mind, the best setting is one which takes the lowered level cap and grittiness of the rules and makes them integral to itself - a land based not on the assumption of super-powered murderhobos, but where even the greatest warriors can be knifed to death in an alleyway, where wizards can murder a village but are next to useless against an army, where dragons are A Big Fucking Deal.
I plan on making a setting on the blog, talking about various techniques you can use to tailor settings to mechanics and how I plan on doing low-fantasy Pathfinder.
Stay tuned for more this week!