The key thing to be aware of is once you get further away from Cape Town the wind isn't quite so consistent and many spots need slightly more specific weather to get the wind (and waves) to make them work.
Paternoster is a possibility - a bit further north of Langebaan. It needs a more south in the wind and the right swell but when it works it has some great clean waves.
Kynsna is another possible option but more like 500km but its a cool place with some good flat water lagoons.
Hermanus is closer to Cape Town - couple of hours drive - wind doesn't blow as strong as Cape Town and a few different flat water spots but also options for waves.
Witsand is about a 3-4 hour drive (Witsand not Witsands next to Scarborough) and is a small village with pretty insane flat water spot. Generally works when there is a strong SE in Cape Town (SE is the best direction in Witsand too). Also waves out on the ocean side of the sand spit. Be warned is known for sharks, not that any kiters have been attached but lots of fish around there so best not to kite around the river month as the sun is going down
If you did want to go further then Cape St Francis can be a good spot (just before Jefferies Bay) as is Cannon Rocks and Kenton-on-sea. I haven't been up there for over 15 years but I remember some pretty amazing kiting.