It's tough to test at home... or small scale at all. Enough time and you might tease it out like folks do with crr on tyres, but it'd be a task looking for such small % without proper equipment.
There is some % to be saved for sure. How much would depend on so many factors it'd be tough to put into cohesion. As ^700w alluded to, Wiggins Hour Record chain was the "best" of a bunch of (already high end) chains that were tested (there's variance in each chain from manufacturing)
If you were very interested in removing as much chain friction as possible, you'd buy an 11 speed Dura Ace chain, have it stripped and treated (lots of different ways to do it... I've never seen anything that was demonstrably better than the old Speed Wax recipe - cheap too!) and run the biggest chainring/cog combo you could. All 3/32 of course.
Hard to say what the difference between that and an Izumi would be... I don't know any tests that have been done on popular 1/8 chains. My guess is there is a fair gain there though... a watt?