This is a long way - simply driving directly to Cape Town, efficiently and safely, would take 2 days. So if you make the return trip in only 2 days you have 8 to do something differently on the way there, which is still limited time. I suggest that you need to pick one area, travel there efficiently, and explore that area in a more leisurely manner. Obviously it depends on what your interests are and where you've been already, however I suggest choosing either the Garden Route, the Wine Country around Stellenbosch/Franschhoek/Paarl, or perhaps Namaqualand. You may be thinnking of a circuit which takes you to Durban, Port Elizabeth, and then Cape Town, stopping at places like Addo Elephant Reserve, Drakensberg, and others, however this is too much in my view. It would take us 3 or 4 weeks for a circuit like this, and you don't want to be spending all of your time on the road.