It would be worthwhile to study the DrawChar routines to see if a (dramatic) speedup is possible.  Switching into and out of wide character mode is quite slow (e.g. spacewarp driving into a star), and emulation of video intensive operations is slowed.

I don't have any specific ideas at the moment, but the fact that the character bit patterns are rotated 90 degrees does surprise me.  Another thing maybe:  color optimized blitting, which may simplify the code path in cases like 'green on black'.

font and draw char were reworked to use a row first implementation.  this greatly improved blitting speed.