I'm kinda old, but I remember when one could earn 7% in safe corporate bonds. My online savings account paid 5.5% in 2007. The economy has been in Oz for so long most people have forgotten what historically normal looks like. Compared to historical norms, we are in an everything bubble.
For an example of someone retired on a half-mil with expenses around 25k, see http://velociraptor.cc. Understand that his approach of using options and CEFs has yet to be tested by a recession, but then again, there he is doing it.
Hey! I resemble that remark!
Seriously though... I retired on a withdrawal rate higher than the 6.45% you are proposing. That situation is a little different as my exit date was 5OCT2012 with a huge federal reserve stimulus program providing a tailwind. Also different, I budget only 25,000 a year and so far have spent less for all five years of ER. Finally, my home is paid for so stache is technically larger than ~500k. I'll also note, I intended to take on part time work for 5-7 years upon ER to bridge any gaps. I was very fortunate with my timing to coincide with the aforementioned stimulus and thus never needed the extra income due to rapid stache growth.
If you insist on doing this:
[1] See if you can get spending under 40k. This will improve your chances while simultaneously supercharging your savings for the final months of stache building.
[2] Sequence of returns risk is going to be huge for you. You are going to need a larger than normal bond allocation. I don't like open ended funds for bonds. When bonds are falling, shares get liquidated resulting in forced selling (at a loss) for the fund. Closed End Funds do not have this risk and tend to hold notes to maturity, e.g. your duration risk will eventually expire. There are lots of CEF funds invested in bonds and/or other debt instruments that yield around 10%. (Else, lots of municipal oriented funds that yield around 6%.) A forty percent allocation to 10% yielders gets you to the 4% rule while leaving 60% of your portfolio available to chase additional income or growth. In your case, the 60% would need to yield 4.08% to achieve the remaining portion of 6.45% withdrawal rate. Completely achievable with a bundle of REITs, BDCs, MLPs, and dividend stocks. But seriously work on number [1] first.
[3] My concept for the remaining 60% of my portfolio not tied up in debt instruments is to sell options. Dividend growth investing would equally valid. The idea is to be income centric. I'm not looking to sell appreciated assets for long term capital gains. I'm looking to generate enough income to cover my budget plus taxes and nominal stache growth thus becomes unimportant. (On the taxes note, recognize my approach is not tax efficient. Getting spending down has helped me live a life where my tax bracket is sufficiently low that I have collected the maximum ACA subsidy three times now; number [1] above is really important and deserves repeating yet again.)
HTH and I'm available by PM if you want something more specific in private.