You'll notice the difference, although as other folks noted above around 15 mph wind drag becomes a more important factor.
It'll be a nicer ride too. Tires with lower rolling resistance are usually more supple and comfortable, especially at slightly lower pressures without sacrificing much rolling resistance. The
rolling resistance tire test site has plenty of data. Tires differ in how much the resistance changes with pressure.
Thinner, lighter butyl tubes will help a bit too. So will latex tubes. Ditto newer tubes like the Tubolito and Aerothan. Or going tubeless.
Aero rims help a bit in some conditions. In cross winds high profile rims can make handling tricky.
Regarding position, riding the hoods rather than drops, with forearms parallel with the ground, is more aero than using the drops, per wind tunnel tests. But it's physically taxing and harder to hold for extended periods. Plan on doing some pushups, planks and core strengthening to hold the hoods/parallel forearms position for long stretches. Riding the drops can be fast if we keep our heads down, but as soon as we look up to check the road ahead it's like unfurling a sail. Everything is a tradeoff between efficiency, comfort and safety.