Dosbox currently supports scaling up to 3x without and with "special effects" (scanlines, RGB raster, etc.).

Will Dosbox support any integer scaling, for example 4x, 5x, 6x and more?

This will be usable for LCD monitors (fixed resolution).

Monitor 1680x1050 (panorama) or 1600x1200 (traditional):
To run text mode 80x25 (640x400): 2x (dimensions of picture: 1280x800)
To run low resolution graphics (320x200): 5x (dimensions of picture: 1600x1000)
To run high resolution graphics (640x480): 2x (dimensions of picture: 1280x960)

You are using scaler up to 5x. The picture will be sharp.

The OpenGLnb surface has two important disadvantages:
- Picture is good only when the width or height of monitor resolution is multiply of width or height of game screen. For example: Worfenstein 3D (320x200) will be good displayed only on monitors: 1280x800, 1280x1024, 1920x1200 (panorama resolutions: fullscreen, 4:3 resolutions: with borders up and down of screen like a letterbox).

- On Windows (randomly?) the Dosbox with OpenGL can break working and display standard Windows XP error message (with buttons "Send it to Microsoft" and "Do not send").