Once you open the pool, you can confirm the filter pressure but with what you have told me and a target of around 17 PSI, here is what I get from the hydraulics model:

Current setup

75 GPM @ 54' head, 1800 watts, 2.52 Gallons/watt-hr

Changing only the pad plumbing to 2"

87 GPM @ 45' head, 1920 watts, 2.71 Gallons/watt-hr

Changing all plumbing to 2"

90 GPM @ 43' head, 1960 watts, 2.76 Gallons/watt-hr

Gallons/watt-hr is the primary metric I use for efficiency so changing the pad plumbing gives you about 7.5% more efficiency. Replacing the suction and return lines only about 2% more. But this assumes that all of the fittings and valves are changed with the pipe.