Capital gains tax is one third of income tax (so a 13.3% max, not 10%), after the R30k exemption.
So if you decided to retire on your investments, and need to sell R600k worth of shares to live on every month. I'll assume you bought the R600k worth of shares 5 years, and they grew at 15%pa. I'll also assume you're now retired and have no other income. Dividends are pre-taxed, so they don't count here:
Selling price R600 000
Less cost price R300 000
=Capital gain R300 000
Less exemption = R270 000
Divided by 3 to get taxable income = R90 000
Tax on R90 000 p/a = R3474 if you're under 65, if you're over 65, you won't pay a cent!
As to whether it's better than an RA depends on many things. RA fees, performance, your current tax bracket etc. I would imagine that from next year, having the ability to put 27.5% of your salary away without paying tax on it is going to be a worthwhile thing to do. Just make sure you put it somewhere where the performance is good, and the fees are low.