You don't necessarily have to get VDSL. It has very limited coverage but you might be connected to one of the latest dslams or IMAX exchanges which supports 20Mbps adsl2+
It almost just as good with a slightly slower upload speed but download speeds are the same.
What about the latency differences between ADSL 2+ and VDSL?
If your exchange supports VDSL upto 40Mbit then do Telkom give you the choice of ADSL 2+ or VDSL?
How does that one work?