TL;DR: having grown up in Somerset West, I only realised later in life that we don't live in the "real South Africa"
I grew up in Somerset West and have lived in the area (between SW, Stellenbosch and Bellville) all my life. One of my friends from university, also from CT, moved to Bryanston recently. He is very happy, but he had to change his lifestyle significantly.
Salaries are generally signifcantly higher, cost of living is slightly lower (although property is significantly cheaper than in most of Cape Town). Traffic is INSANE. I drive between Somerset West and Bellville (N1-R300-N2) every morning and it's a breeze compared to a good day in Joburg.
Money is great (I get offers for nearly double my current Somerset West salary on a monthly basis), but, personally, Joburg would make me so miserable, no amount of money in the world would be able to fix me. Every time I travel to Gauteng for work, I realise how lucky I am to live in the Western Cape. But obviously that's just me. If you like the "big city" vibe, and wouldn't miss the scenery, wine farms, the beach, hiking etc., your experience may differ.
Oh, and one last thing: something which gets me every time, is the fact that stores close unbelievably early in many parts of Gauteng. It's like everybody goes to sleep at 7pm.