i'm confused myself. looking at MMC's own site you'd think there's more difference between a 4/4 and a Plus4 than a Plus4 and Plus6. i so wanted to love it and consider it for myself, but in the flesh.... it's a Plus8. i've just looked at wikipedia and Parkers, everyone quotes different widths!
It was launched as the new wide bodied car. This is from Autocar.
"The new CX chassis provides around 20cm more cockpit length to accommodate bigger drivers, allows bigger doors and leaves decent luggage space. The car’s length and width are almost identical to a Plus 8's, but the wheelbase is 18mm longer".
Looking at the pictures online there does appear to be two holdalls comfortably fitted behind the seats, which is twice as much as a Plus8, unless you get the boot conversion from Morgan Park DE, which still only allows for one bag really or ideally the side screens without a sidescreen bag.