Y'all don't see that OP is looking to arbitrage on the BTC price. It's an easy 20-30% profit, easy being subject to international money transfer regulations
This is exactly what he's doing, and SARS & SARB already know about this trick. There are two problems with doing it:
1) It is in contravention of exchange control regulations (they call it a "loop structure" and it's explicitly not allowed).
2) When they pick it up (and they do eventually, trust me), you will get nailed with marginal tax rate on the amount received in your bank account,
without being able to offset the cost of the purchase of the BTC overseas.
So you buy R500K worth of BTC overseas, send it back here and R600K goes into your bank account. Suddenly you're smashed with 45% (or whatever your marginal rate is) on that R600K.
The above is the reason there appears (at first sight) to be an arbitrage opportunity. If there is one, it certainly isn't via your discretionary/foreign investment allowance.