The new 1.15 version support 1600x1200 resolution.
I wanted to give it a try but opening FDM1200R.EXE or FDM1200D.EXE I got those error messages :

FastDoom VBE 2.0 direct modes only support 8 bits per pixels
Compatible VESA 2.0 video mode not found! (1600x1200 required)

I have tried both with DOSBox and DOSBox-X
I used default video card which is svga_s3. I have also tried with vesa_nolfb, vesa_oldvbe without success.