3 special African countries together are limited by per country quota (up to 3850 per country), that is 11550. That is about 55% of the total number of African visas. So, African visas from other African countries are still 45% of all African visas. So, total speed up could be 100/45 = 2.2 times. That is why even if all 3 special African countries are reached, 20K per month increase is hardly possible.
We actually have Ghana too, even though Ghana does not have a special cutoff, but it has a limit.
If, however, we consider Asia after both Nepal and Iran are reached, the speed increase should be huge, because Irani + Nepali visas could constitute about 80% of Asian visas, so other countries constitute only about 20% of Asian visas (5 times speed up)