I'm sure you know this by now, but a typical seven string light gauge set goes 10/13/17/26/36/46/56 (or 59). But whoever came up with those gauges was, to put it bluntly, wrong.
There are some major tensions issues that arise, specifically with the 13 and the 46. If you've played one of those sets, you've probably noticed a dip in tension on those two strings, making them feel all loosey-goosey.
On our set, we use a 13.5, a 48, and a 60 for the 2nd, 6th, and 7th strings, respectively, in order to bring the tension up on those strings to match the strings around them.
This results in a set that feels tighter, sounds powerful, and stays in the tune better. Who wouldn't want that?