byuu says:

Changes: HD mode 7 supersampling support, HD mode 7 mosaic disable option,
various HD mode 7 bugfixes, default waveOut audio latency to 128 instead of 512,
removed 512x240 hires mode 7 mode.

There's also a small experiment, making this release a beta release as well:
for a large speedup, when in EXTBG mode, I'm bypassing rendering BG1 for a
performance boost. EXTBG is only used as a priority layer, and is overwritten by
BG2 except in one extremely pathological case.