I am not an expert but my answer is no.
Everyone defines risk differently, but a lot of people argue that the standard deviation itself is not a risk, the behavior as a result of the fluctuations is the risk
1. A lot of the proponents of a 60/40 split think it is risky to have a high standard deviation because you will bail out if you have a 40% drop in your portfolio. The risks aren't in the market but in the person reacting to it.
2. Warren Buffet thinks the biggest risk is inflation, which will eat up your bonds. He advocates for a 90-10 split (although people have parsed his missive endlessly, I think the consensus is 10) probably because he has weathered so much and he cannot fathom there are people out there that would be selling, and not buying, on a dip. JLCollins thinks similarly and he is 88 total market / 12 cash...
3. Swedroe looks at matching the risks of your investments to the risks of your income. He looks at people who have "bond-like" salaries and "equity-like" salaries. According to him, bond like salaries belong to people whose salaries aren't affected by the economy (a teacher with ten, a doctor) and equity-like salaries belong to those very tied into the economy (salesman, entrepreneurs)... He advocates less risk for the people with "equity-like" salaries because their success is tied to the market which means they are at risk of a double loss in the even of a depression/recession/event. (the risk is measured both as large vs. small and growth vs value... Large Growth which the TSM/S&P500 funds tilt toward are less volatile than Small Cap Value indexes. It sounds like you are an entrepreneur so I believe Swedroe's book ("The only Guide You'll Ever Need To..." would urge you to avoid small and value factors and stick with a Total Market index... )
4. There is also a Buffet/Bogles vs. Bernstein/Swedroe decision on the need for international holdings. This debates involves a lot of factors but I think the question I always come back to is whether the international holding increases return or merely eases volatility. Nobody knows that answer, but a lot of people have ideas.
5. Everyone loves the Total Stock Market vehicle, but you will find a lot of critics of the Total Bond market index funds. 1) They have some corporate bonds which are correlated to the stock market. 2) They carry some risk. Bernstein, Buffet and Swedroe all prefer an ultra-safe Short Term Treasury fund instead. There isn't much return, but even though the three have a different percentage allocated to the Treasury fund, they all peg that percentage to money you will absolutely need. So Buffet (and Collins) think you need about 10-12% or so of your invested money specifically to weather a 3-5 year period when the stocks are down. Bernstein likes 25%. But they all advocate not thinking of bonds as an investment but rather as a safeguard, while the stock side does the work. Only you can know what percentage of your portfolio that would be.
If you do want the added value from the fixed income side, one quick tweak to your 80/20 TSM /TBM would be to substitute an intermediate term treasury fund for the total bond fund.
They look almost the same in a vacuum (per portfolio visualizer 1987-2016:
TBM 6.18% return, 3.83% STDDev
ITT 6.37% return, 4.85% STDDev
Pretty similar... But because when stocks drop the money moves to Treasuries, it pairs better 80/20 with TSM:
TSM/TBM 9.31% return, 12.38% STDDev
TSM/ITT 9.41% return, 12.22% STDDev
The Treasuries are less volatile when paired, have better return, and I don't pay California state tax on them which means it is worth considering holding them in taxable accounts. No way to measure it but I would guess that getting to put more equities in tax-advantaged accounts will increase the old number fast.
So, super long... Sorry. I would:
1. Evaluate how capable you are of completely ignoring the market (the more ignorance the less of a danger you pose to yourself...)
2. Figure out how much you need to ride out a 3-5 year drop.
3. Figure out how safe your income stream is.
Those three make up your fixed income term/type and percentage.
4. Make a decision on international.
5. Evaluate Total Bond....
If you're like me you'll think all that through and then circle back anyway, but at least you'll have confidence in your decision since you thought it out.