Not the greatest picture but it should get the idea across:
That is 20% over the factory (ends up begin approx. 5%), 20% on the fronts and 20% across the top of the windshield.
I have tinting the back of my last 3 SUVs this way...the kids do not complain at all then about the sun. They can still see out just fine in the daytime, too. Just my $0.02, but I have been installing tint professionally for almost 7 years (own my own business) and I prefer the front doors to be slightly lighter than the rear windows. Gives it more of a graduated look going from the clear windshield, darker fronts, and even darker rear windows.
I would not go 5% over the factory...it won't look any different from the outside but will be much, much darker on the inside...too dark if you ask me. Also forget about seeing anything at night out the back.