Performance during a downturn has been a question mark in my mind for performing notes. 9-10% yield without volatility (like the markets) sounds nice but if even a fraction of the note portfolio goes non-performing then it darkens the whole picture, even makes buying stocks/bonds look like the better option again.Is this a fair assessment?

Way too volatile to be collecting as rent. 

People want to get it out of the volatile market and put it into something stable and inflation resistant: cash-flowing real estate in flyover states.  

It's a very highly volatile market so before you make that dive you better know what you are getting into, it's certainly not for the feint hearted.

@Carlos Feliciano II  It really depends on how much volatility/risk you are willing to tolerate.High Yield Savings accounts have the best Risk-Free rates...but they are low. 0.7-0.8%.

I've found it to be much more volatile.  

I didn’t like the stock market volatility, so I decided to leverage my 401k proceeds to set up a Self Directed IRA to invest in Real Estate rentals.I have $650k available and looking in the DFW, Jacksonville, Albuquerque and Colorado Springs markets for SFH or Multi Units.My question is:Should I purchase properties via cash or leverage financing and incur the UBIT taxes.

Remember that higher returns, whether actual or proforma, almost always translate into higher risk and / or volatility.  

This can be a great way to mitigate risk and stress of stock market volatility knowing you have steady income outside the market that should not only be minimally impact by temporary market recessions/corrections but that should see steady increases throughout your retirement. 

If I held this property outright, it would swing to 60% cash flow, 40% expenses, so I think that gives me more security, especially considering the volatility of this market.