Can somebody recommend good DOSBOX settings to make History Line run smoothly? With the default settings, the animations are awfully slow, in particular fade-ins and -outs.

I am playing it and I am content. Here are my graphics settings from the configuration file.
You can try to change the "output" setting, it has the biggest impact.

[sdl]
fullscreen=false
fulldouble=1024x768
fullresolution=original
windowresolution=1920x1440
output=OpenGL
autolock=false
sensitivity=100
waitonerror=true
priority=higher,normal
mapperfile=mapper.txt
usescancodes=true

[dosbox]

language=
machine=svga_s3
captures=capture
memsize=16

[render]
frameskip=0
aspect=false
scaler=normal2x