Because of the water features and vac line, you will need heavy flow some of the time. This means you have two choices, multiple pumps or a 2-speed pump. For a 2-speed pump, the turnover time is twice as long as that of the high speed but the energy use is about a third. So overall energy savings is about 30%. Going form a 2.5 Hp to a 1 Hp pump will save you close to the same (depending on pump) but you may still need a bigger pump for the features and vac. So either way, you should have significant savings which will pay for itself in not too much time at all.