The bond premium (Spread values) between the bonds of the two currencies are as depicted in the graphic for the various maturity terms. The market is King and if the above is the spread each individual investor must make their own decision. I for what it may be worth, will back the rand as an investor/trader.
A quick Google search will tell you that a bond’s yield relative to the yield of its benchmark is called a spread. The spread is used both as a pricing mechanism and