Up until now, I've always played DF on my 1366x768 monitor, windowed, maximized to fill my screen and with the defualt ASCII. I've never had any sort of issues with distortion or blurred "spites", and I'd like to keep it that way. I'm considering an upgrade to a 1440x900 monitor, but I've heard various gripes on the forums that larger monitors will distort the game quite heavily.
So basically, for anyone who plays on a 1440x900 or larger monitor, is there actually distortion?
The short answer is "probably not if you set the correct settings"... but that's a bit tricky, and some hardware combinations work better with some sizes.
First off, are the monitors you are talking about old-fashioned tube monitors, or LCDs (aka "flatscreen")? Tube monitors are far less "locked" into a specific resolution, due to their construction (or, depending on your point of view, they're a bit fuzzily analog at any resolution). LCDs will generally look best when used at their actual hardware resolution; if set to other levels, they may show some aliasing or ghosting.
Do you know what resolution and DF settings you currently use? The truly default windowed setting would be 80 x 25 characters, using an 8x12 font ("curses_640x300"), for a natural resolution of 640 x 300. The other default, used for full screen, is 80 x 50 characters, using a 10x12 font ("curses_800x600"), for a natural resolution of 800 x 600. (The easy way to tell which you are used to is that the 640x300 set has round dwarf faces, whereas the 800x600 set has dwarf faces with pointy beards.)
It's not clear whether your monitor and/or graphics card is auto-adjusting to an appropriate size, or you have DF set to put in more tiles. For instance, un-resized 10x12 characters on the 1366 x 768 you mention would give you about 136 x 64 characters.
To look at it another way, if you upgrade to a higher-res monitor, do you want *more* tiles, or *sharper* tiles, or the *same* tiles but possibly with some resizing artifacts?
Personally, I pick a font that I like the look of, then do the math to have the right number of tiles set up, and black space set so if the borders are a pixel or so off it doesn't distort. I usually play DF on a (6+ year old) 1920 x 1200 LCD monitor, typically with either an 18x18 or 20x20 font, and it looks great. I suggest having a look at the
tileset repository on the wiki to see what you like.