this is the best climbing website in SA....
cape town winter is rainy season; if raining no climbing; if no raining great climbing
a few sports crags within 30mins from CT with the grades you are looking at; Silvermine is your best bet.
Montagu (town) is fantastic - 2hrs drive from CT; worthwhile to go there for 2/3 days; unfortunately there is access problems to the area with the best crags in your grades (Boschkloof). Montagu gets very little rain; often when CT is wet montagu is good
when up north Boven is THE BEST spot for sport climbing. kid-in-a-candystore stuff.