Couple of things.  First, you should show your charted results for the CPP/OAS at 65 scenario to support your claim of the couple being $10K short over their lifetimes.  Second, although your math is 100% sound in the examples you have chosen, have you considered and tested all combinations? ex. deferral at each year between 60 and 70, different lifespan assumptions for each as there are no lifespan guarantees (although that may be good reason to defer CPP/OAS and use your own capital) and, not to be underestimated the impact of taxation.  This strategy may not be optimal for some tax brackets nor for all family health histories.  Admittedly, there are thousands of combinations, but the computations are simple and could be easily handled with an excel macro or better, Matlab, to produce a net present value result for each.