Using your x2 factor from your mix of loans can't really be equally applied to my mix, but using my current values it works out at 1.59%/22.79% = 6.977%, which in theory works out at $1590 pa for $100K. Using your x2 factor, gives $3,180. Will have to wait and see how it works out.

Note this doesn't factor in lower interest achieved due to defaulted loans, nor does it factor in increased interest from reinvesting... I'm tempted to write a simulation if I ever find the time...

Based on the above and my tax rate etc., I'd still be earning 13.8% (not considering reinvestment). I'd be very happy with that