Nice article. A couple of comments.

Your first paragraph suggests that the Federal Reserve has been increasing the prime rate. For clarity, the Prime Rate is a market determined rate that commercial banks charge (usually corporate) customers. The Fed meanwhile controls the discount rate, a short term institutional lending rate for borrowing directly from the Fed.

Second, and perhaps more important, a blended average interest rate won’t show the potential impact of rising rates on a client’s monthly payment. It may be more useful to model both mortgages against the index of the adjustable, up to the interest rate cape (if it has one).

In the end, I’m not sure a lender is the most qualified to do this sort of analysis. A fee only personal financial advisor is probably better suited, but watch for those who only offer prepackaged solutions.