what exactly is the difference between the two ROM's? Does OS X even support the compute ROM?
I don't have this card, can't tell.
If you want to, you can dump the ROM out to have a look.
Anyway, most likely just ~2% clock difference (e.g. 1366MHz vs 1340MHz), or the fan profile is more aggressive in gaming mode etc.
There is NO difference in macOS support. You can use either ROM you want.