Matt,
There is a thread here on AH (I can't find it right now. Maybe someone can help.) that says the Zimbabwe elephant population is 85-100,000. (This info is fairly current) Rhodesia said they had a carrying capacity of 46,500 elephants. I don't think Zimbabwe has ever updated this so the 46,500 number is 35+ years old. The human population has increased from apx. 7m to 14m in the last 35 years. The actual elephant carrying capacity is probably less than the 46,500 figure if you factor in the increase in human population.
The carrying capacity of Hwange NP increased from 2,500 elephants when there were no boreholes to 10,000 to apx. 17,000 as wells were added. These were Rhodesian numbers. Again, 35+ years old. The Rhodesian's weren't able to carry out the culling program very much in the 1970's due to the bush war. There are now apx. 40-50,000 elephants in the Hwange area plus more than that across the border in Botswana. A PH in the Hwange area told me that if all the elephants in Hwange were culled, they would probably be replaced within two years by a migration from Botswana.
I am going from memory on these numbers, but should be pretty close.
Botswana's elephant population is even higher.
I read something this year, (possibly here on AH) that said RSA looked into culling some of the elephant in Kruger. The greens got wind and threatened RSA with a boycott of their wine and tourism.
If something isn't done soon, Botswana and Zimbabwe are going to have a catastrophe that will make Tsavo in the 70's mild in comparison. A two or three year drought in Botswana/Zimbabwe may have dire consequences.
Any type of culling program now would bring down worldwide condemnation. The animal rights people don't understand it but they are creating a disaster.