So I've been here for the past 4 days and its looking like we're gonna have an awesome season.
I'm 99kg (220lbs) and I do ride a surfboard so my kites are a little smaller but so far its been 6m weather everyday with one day on my 5m. I did use my 8m for an hour but then it picked up and 6m was perfect
What you need to understand is the wind picks up through the day so you can get away with larger kites (that will be 8 or 9m in Cape Town) but you need to be on it and get out as soon as the wind starts to pick up - that might be 9am some days but other days it will be 5pm. You may get an hour when you can use bigger kites or it may fill in slowly and you'll have several hours. It really depends on the weather. Some days will be 5 knots all day and then at 6pm, within 30 minutes its blow 30 knots. Its a crazy place but you are guarantee a lot of great kiting.
Overall, smaller kites are a better idea as you can generally just wait until later in the day and get a session it when its pickup, with bigger kites you just need to be ready to get out as soon as it fills in. Ideally bring as many kites as you can
Brian from Suntrax posted a link above to a blog post I wrote a couple of years ago and I've been updating each year. (Thanks Brian!) I've been coming to Cape Town, on and off for 12 years, I love this place and it is one of the best places in the world for kiting, you just need to get your head around how the wind works and then you can get so much out of kiting here.
Here's to a windy and wavey Cape Town summer!!