The aircraft does use a lower equivalent altitude in the cabin, while usually operating at an altitude higher than most other aircraft. Since it's designed for it, and I don't think it makes a difference it fuel consumption hence there's no reason to opt out. It's highly appreciated by crew and passengers alike since it leaves them feeling more rested and less jetlagged. It's around 6000 feet rather than the usual 7500-8000 feet.
What also contributes substantially to passenger comfort is the fact that the air is considerably more humid, since corrosion is less of a concern, also leaving passengers and crew dehydrated.
I've never flown on one, but it seems to be holding:
"As for the cabin pressure and moisture, it's all true: I arrived both
times feeling well-hydrated and without the parched skin that would
result from flying in any other airplane."
and a little more on the workings of this system:
"Cabin – Pressurization differential pressure maximum is 9.4 psid, so
the cabin altitude is only 6000 feet when at the max cruising altitude
of 43,000 feet. There is a cockpit humidifier switch, and cabin air
humidification is fully automatic." Source
and here's an article from 2011:
Most conventional passenger jets set the cabin pressure at an
equivalent of around 7,500 to 8,000 feet above sea level, which Boeing
claims is the primary cause of a range of in-flight ills. “There are
many passengers problems associated with altitude – headaches, muscle
aches, fatigue and even nausea” Craver says. The difference between
external air pressure when an aircraft cruises at 40,000 feet and an
internal pressure that’s one-fifth of that stresses the plane’s
fuselage – and the greater the difference, the more the stress. That’s
been the limiting factor in increasing cabin pressure, Craver
explains: the metal body of current aircraft wouldn’t safely be able
to handle the fatigue induced by maintaining this pressure at high
altitudes. That changes due to the use of carbon-fibre composite
materials on the 787’s fuselage. Carbon-fibre doesn’t suffer from
metal fatigue and in turn allows for lower 'cabin altitude' levels.
The 787’s cabin pressure is set to 6,000 feet, a figure arrived upon
by Boeing modifying a pressure chamber to look like an airplane cabin
which could hold 12 people at a time. “We cycled over 500 people
through the chamber, and they stayed there for up to 20 hours of
simulated flying time” Craver recalls, and they found that 6,000 feet
was the ‘sweet spot’. “Between sea level and 6,000 feet there was
almost no difference in the reported symptoms” Craver says, “so we can
alleviate or mitigate a lot of symptoms you get at a cabin altitude of
8,000 feet” Boeing claims that one in four travellers experience some
form of ‘respiratory distress’ after flying 12 hours in a conventional
aircraft with a cabin pressure of 8,000 feet, but this plummets to 5-6
per cent at 6,000 feet.