I just find it odd that some games will respect aspects and others not, regardless of dosbox's aspect= setting. There has to be a reason.
aspect=true only affects game resolutions that have a vertical dimension of 200 or 400. If aspect=true, then those are corrected to 4:3. Beyond that, Dosbox assumes square pixels, so if you set Dosbox to output 1680x1050 (or any widescreen resolution) with aspect=true, you will _always_ get black bars on the sides.
If you have aspect=false, then you will get black bars on the sides _unless_ the game uses 320x200 or 640x400 (or 320x400 or 640x200), in which case you will get no black bars on the sides when dosbox is set to output a widescreen resolution, but you will get black bars on the top and bottom if dosbox is set to output a 4:3 resolution.
If you set aspect=true, fullresolution=1680x1050 (or whatever your display's native resolution is), fullscreen=true and output=ddraw then every game (except text mode) should be zoomed correctly (pillarboxed - black bars on the sides) and your driver settings shouldn't have any effect because those (the driver's) settings only affect non-native resolutions.
If you want your dosbox games zoomed without respect to correct aspect (i.e. fill the whole screen), then set aspect=true, fullresolution=original (or any 4:3 resolution), output=ddraw, and set either your drivers or your display to zoom without respect to aspect. Dosbox won't scale your 4:3 games to fill a 16:10 screen* - your drivers or your display will have to do that.
* except text mode and when aspect=false, 320x200 and such just happen to be 16:10.
My advice is to always use aspect=true, except when using fullresolution=original and scaler=none or any 2x scaler.
If my post is incomprehensible, try the suggestion in my third paragraph (fullresolution=1680x1050, fullscreen=true, aspect=true, output=ddraw) and report back which games behave incorrectly (i.e. aren't pillarboxed).
All my info is based on testing (I tried various combinations with Blood, which has plenty of different video modes), not reading (and understanding) the source code.
Maybe we should give you build that will list the screen resolution dosbox thinks it needs to match the settings and the resolution it actually got from sdl/directx. then we have hard and concrete numbers.
It'd be great if dosbox printed the video mode in the console whenever switching modes.
edit: looks like I could just uncomment a bunch of LOG_MSG lines and compile myself.