It would take several days to execute the adds directly. To emulate the adds in 65816 would make it days weeks or months to complete.

Here is an 8-bit ADC/SBC BCD + flag test from blargg:

Passes in bsnes v061r02 with the updated algorithms.

Fails in bsnes v061, Snes9X v1.52, Super Slueth v1.04f, SNESGT v0.230b6, MESS v0.136, and ZSNES v1.51.