Yo! So, Cruisers 7 is 3cm (1.2") longer than Cruisers 6. That's about the only difference. I've actually managed to stretch the tapes on both of them to a full meter (40-41") apart. That does take practice, though.
It's worth noting that Cruisers 7 is the same size as Baby Dry 6 and Luvs 6, both of which are considerably easier to find in stores than Cruisers 7. The elastic on the Cruisers is slightly stretchier, but that advantage has eroded over the last two years, and is discernible only in extreme cases--like me, trying to stretch into them with 44" hips.
So you might try Baby Dry 6 before you bother ordering Cruisers 7. The differences are very, very small. As for whether that 3cm of extra length will help: It depends. If this gets the waistline of the diaper closer to your actual waist, then you'll probably be taping around a smaller part of your body, meaning you'll get a better fit. In theory. 3cm ain't a lot, though!