Without knowing the true delivered heat cost of each system it will be hard to compare. Once you have an idea as to what the true operating efficiency numbers are, plus the delivered cost of energy, you can input some basic data at: http://www.warmair.com/html/fuel_cost_comparisons.htm
Heat pumps decline in heat output the lower the outdoor temps drop and operating efficiency drops too. But, unlike any other method of heat a heat pump gives you more than it is consuming until its breakeven point. This is measured by its COP (Co-efficient of Performance) in which the amount of energy it is consuming is compared to the heat (energy) it is putting out. So the COP drops and once it hits 1 there is no benefit in using the heat pump as a heating source. Most VRV/VRF manufacturers provided extensive data on the heat output and the electric consumption of their systems at numerous different temps.
Based on your location it would likely make sense to use the heat pump as your primary heat source and the hot water as a supplemental heat source once the heat pump can no longer carry the load on its own.
With my home the heat pump can provide the required heat to about 14*F but then electric heating coils located in the ducts just down stream form the air handler cycles as needed to maintain the room temp. Heat pump continues to run and produce heat and the electric coils supplement the heat pump as needed.
The VRV/VRF systems produce more heat at lower temps than conventional heat pumps. I am pleased that my system can produce virtually all the heat my home needs. Our winter design temps are 9*F. The number of hours we spend below 14*F where I need supplemental heat is minimal.
Also, as a consideration, while not a VRV/VRF system you may want to consider this system form Mitsubishi. It produces 100% of its rated heat output down to 5*F and at -4*F it is rated at 90% of its output. http://www.mehvac.com/UploadedFiles/...0Submittal.pdf