I don’t think anyone can predict what interest rate conditions will be like in five years. It's easy to predict short term rates are going to rise, and directionally we know where long term rates are headed, but the magnitude of those changes is unknown. I once did a back of the envelope calculation on long term rates using empirical research and data on the relationship between the fed funds rate and the 10 year treasury. The 10 year Treasury has always been anchored by the fed funds rates and spreads have consistently been 200-300 basis points over a 20 year period of time. The 10 year treasury tracks the 30 year fixed rate nicely. I think my calculations showed that even with really aggressive interest rates hikes by the Fed it would only result in a maximum 30 year fixed rate of about 6 percent in 3-5 years (using the 10 year Treasury as a proxy).
I would tend to think about this option you raise in terms of return on equity. How much equity do you have generating $5k/month? If you deploy this equity in another investment vehicle what type of returns do you hope to achieve? If you set these two scenarios up with ROE being your comparison metric you can then run a sensitivity analysis on rates to see how it affects your decision.