Why do background sections bob up and down by one pixel? What's the 'magic bullet' feature that once emulated fixes most of it?
Exact cycle timing of PPU internal register copies vs. CPU writes is one thing. Exact cycle timing of mapper IRQ generation or sprite 0 assertion vs. PPU memory accesses is another. Are you talking about sprite 0 splits or MMC3 IRQ splits? How far is your emulator from passing
blargg's MMC3 and sprite hit tests?