There are lots of places closer than Boven...
Bronkies is a very nice crag just outside Bronkhorstspruit, and there are some great climbs within the range you have specified. If you take the Witbank highway you should be there within about 40 mins, expect to pay some toll fees (think its R18). Or take Lynnwood rd heading east, at the T-section turn left and then turn right to the crag (think its the last turnoff before you reach the town). Rather use a good map, it helps! The land owner prefers climbing during weekends, pay entry fee at the big house (usually R10 p.p). Very easy access and close by parking.
Chosspile is the crag close to the damwall of Hartebeespoort dam, about 30 mins from Pta if you take the highway . Go check out www.saclimb.co.za
for route guide and directions. Parking is a bit far away from the crag, and the access sucks.
Strubens Valley is urban crag in Jhb, or Roodepoort to be more specific. Again check out www.saclimb.co.za
for route guide and directions. Routes are short and very close to each other. Parking is nice and close by and the access path is very easy. Best to take the R28 Krugersdorp Highway instead of the N1.
There are more places but I think you should find some nice climbs at the above mentioned crags.