In my opinion, using a valve to restrict the flow is not a good choice.And if you get with the flow restriction valve and cut the power consumption in half, as I was able to do with my system, you get.
Savings per month $30
Break even: 13 days
Total saving over 120 months: $3600
Savings are there for those that, for whatever reason, have a single speed pump.
I don't think that you could get the power to half without cutting the flow to basically zero.
Going to a smaller impeller would be a much better option to reduce power and flow.
You can go to a two speed pump or variable speed.