I can't recall, have you been to RSA to hunt?
If you haven't, this is where things get tricky. The outfit I hunted with when I went had properties that were a bit more "domesticated" and then some that were very large, and very wild. The domesticated properties, looking back, were rather small and the animals didn't seem to react as quickly to human presence. Then we hunted 30,000 acre properties that took an hour and a half to drive across and that was only covering one small piece. Those animals you'd see for a second, then gone. We had to put a challenging stalk or two on them there.
Red Lechwe are definitely more put and take outside their range than gemsbok. Lechwe spend most of their time near water. If you see one in the middle of a property without any real appreciative water, they are generally out of their element.
Gemsbok, from what I've seen, adapt a little better. They are more suited to what you'd probably see in Free State. They are tough, generally not that keen on humans (regardless of the property), and will be a little more sporting.