If you are willing to invest in stocks, history suggests (but does not guarantee) that would be better yet.
Depending on your investment horizon, and risk tolerance, the longer you are willing to keep the money in stocks, the closer you are likely to come to realizing the long-term performance.
Many here might argue to put the whole 675K into an index fund at once, and that would probably be the best advice, historically. But it can be psychologically difficult to maintain the discipline if a downturn occurs immediately thereafter.
Here's a suggestion to get your feet wet, while allowing your own risk-psychology to adjust over time.
Divide your wad into 24 chunks; $28.125K each chunk. Then put one chunk into the market every month, for two years. On down months, increase your chunk for that month, say by 15%, and re-balance the remaining chunks. On up months, do the opposite; i.e., reduce that months chunk by some percentage, and re-balance the remaining chunks again.
At the end of two years, you will be fully invested at a dollar-cost average price, and you will have had time to acquire a realistic perspective of risk vs reward in stocks as compared to a
"safe" (but paltry) 1.25% in a savings account. The S&P 500 pays a dividend higher than that.
For whatever it's worth, my
"gut feelings" have cost me far more real money than any I would have ever lost in a broadly diversified market move downward. A market move down only costs you something if you sell when it goes down.
If the percentage of your business funded by debt is generating income faster than 3.95%, I would be inclined to keep that debt, and just let the business pay it off over the course of time. Depending on future circumstances and opportunities, it might even make sense to take on more debt.