Clicking the "Backbuffer in system memory" check box on
the Display Setup menu will improve performance on some
computers without 3D hardware acceleration. Only enable
this option if you experience severe frame rate problems
when viewing transparent glass and water. This has to do
with your video card's memory access speed. This feature
is not compatible with all video cards and may cause
problems on certain systems if enabled.
Min texture size was a way to get around a limitation on older cards with, you guessed it, minimum texture size. 3D cards in the mid/late '90s had lots of quirks. A usenet search found info about old Riva 128 cards needing this to be set to 4 to fix texturing problems, for example.