If one of bonds/eq always outperforms bank account, then yes i should invest most of my savings. However, this is a big IF.

Should I invest 80% of my USD, leaving just enough (20k) for Oanda trading and conversion?

(SGD? need to leave enough in bank accounts.)

In a crash, I think bonds (HY? less confident) might perform reasonably well. Gold (not gold mining stocks) is another asset class that has a chance to stay resilient.