I think you will be safe with a 50% vlt tint like sold at pepboys and online. Ebay has a lot of sellers who sell precut tint and special requests such as tint shades ie gray, tan, smoke, mirror, etc.
Most cops eye ball your tint from the rear, so the lighter tint should be on your rear and driver window. Then the rest can be darker. My sidekick has 2.5% vlt on all windows but the drivers and rear. Driver is 20% rear is 35. I get the attention of cops, but as they come up behind me they can see through my sidekick so to speak and move on.