I ran a series of timedemos again, and they've improved quite a bit since v0.6. It's running above 40FPS now!
I never tested 0.666 so I don't know which release gave the biggest speed boost. If you want to know, I can test 0.666 as well.
System: Am486 DX4 120MHz, no L2, 16MB, Tseng ET4000/W32 1MB VLB, ESS ES1869
Fastdoom 0.7-RC1, 386 exe, real mode, no driver TSRs, with audio:
demo1: 1461 realtics (40.484 fps)
demo2: 1879 realtics (43.358 fps)
demo2: 2928 realtics (46.088 fps)
Fastdoom 0.7-RC1, 486 exe, real mode, no driver TSRs, with audio:
demo1: 1470 realtics (40.356 fps)
demo2: 1884 realtics (43.300 fps)
demo3: 2933 realtics (46.048 fps)
Am486 DX4 120MHz, no L2, 16MB, Tseng ET4000/W32 1MB VLB, ESS ES1869 + Yucatan FX /// 5x86 133MHz, 256kb L2, 64MB, S3 Virge/DX 4MB PCI, SB16 /// Pentium III 1GHz, 512MB, Asus V7700 64MB AGP, SB Live!