It appears to be very difficult to a cost-benefit analysis of faster payments:
"Although we cannot provide monetary estimates of the benefits of the U.K. FPS, the total costs of the new system relative to the U.K. population (63 million in 2012) suggests that the value of benefits per individual per year need not be large to give FPS a positive net present value." Green et.al. FRB Boston
More so because it is difficult to calculate possible external benefits to non-bank payment providers who can hook up to faster payments (at least in the UK there is a way for them to do so).
Here is an example from Transferwise which claims to be the first Fintech company to hook up to the UK Faster Payments Scheme.