One of the problems with "internet based" research is that not all of the information you'll find is accurate - I don't recall ever seeing an official published spec for ground clearance, but having said that, for some reason the figure 7 inches sounds about right to me, 8 inches is more than I expect
Regarding the rear diff to ground clearance, that may not be the lowest point on the vehicle, but, like I said earlier, that is dictated by the wheel/tire size, so you can check the tire placard in the driver's door jamb, and once you're running the OEM size tires at the recommended pressure, whatever you measure is what it is, unless someone has replaced the rear axle with a different, non OEM one, which I think is unlikely - it's not impossible, but, since the front & rear axle ratios have to be matched, it's not a trivial modification. Switching to a taller tire will increase the clearance here, but be aware that anything larger than about 29" will probably rub on the frame at full lock - my tires are 235/70R16 (a hair less than 29") on OEM alloy rims (I have a 98 Grand Vitara), minimal trimming of the plastic wheel arch liner was required behind the front bumper, and on full lock they will just "polish" the frame toward the back of the wheel arch. OEM tires, at least for the GV are a 27", so these do give me roughly an inch more under the differential.
Regarding lifts, a two inch lift is about as much as you can (or should) consider - more than that will typically put the front CV axles at risk, unless you drop the front diff to compensate, and can cause camber issues - if you feel the need to go taller, you'll need a lift kit that deals with these issues, and yes, Altered Ego makes one.