Yeah, at 1280 x 1024 I would also second MED to MED-HIGH.
- Maybe with 2 x Anti-Aliasing even since it's a low res.
HIGH on a video card with a 128-bit bus in any ARMA II MOD might be asking a little bit to much of it, but it certainly won't hurt to try. (I understand DayZ to be even heavier than the original game).