"Some sources estimate that between 11 and 17 million slaves crossed the Red Sea, Indian Ocean, and Sahara Desert from 650 to 1900, compared to 11.6 million across the Atlantic from 1500 to the late 1860s. The Arab or Middle Eastern slave trade continued into the early 1900s." Teribus Date: 01 Dec 06 - 08:03 AM

So, let's see.
Average of 15 mill 'Arab' slaves in 1,250 years, compared to 11.6 mill Trans-Atlantikers in 360 odd years.
Going on those figures, Transatlantic Slave trade would only have needed to have existed for another 106.25 years, hitting the 15 mill mark in only 466 and a quarter years, leaving seven hundred and eighty-three (and three quarters)

11.6 million for 466, declared.
The Arabs were all out for 1250.

Read the scores on the boards, Teribus, old lad.