Be careful not to confuse [how material is captured] with how it is mixed ie [the final context] - one obviously informs the other but making a foley track that is "gritty and real" sounds to me like a lot of very careful, layered, detailed foley tightly edited & predubbed to follow picture cuts and perspective changes tightly...
The films you use as examples would have had excellent, very experienced foley artists working in large foley studios with a LOT of props... and I think that is key to creating a great foley track - the right sounds & performances, the attention to detail etc...
I'm not sure it is really realistic to do the intense, detailed performance work to picture in an exterior location... I'd bet the foley predub for Hurt Locker involved a lot of tracks, and for sure was augmented with exterior FX recording, but foley is about performance to picture....
I'd use the KMR81... We've never had a problem matching exterior foley to production sound using this mic... But how well it matches exterior scenes is dependent on how good your foley room is - is it a large room with neutral acoustic? Do the pits sound solid ie dirt sounds like dirt? (& not like dirt in a wooden box) You could also try recording two track, the KMR 81 close and another mic wider, to give you optional perspective in the predub...
Having a creative foley artist & the right props to achieve this will be VERY important - dirt & debris, weapons, plants, bushes etc....