I unbolted the 17x9.5 5 1/5" back-space wheels from my Satellite and bolted them up to see how they fit. These tires are 275/60/17's and measure almost 30" tall.
The true 5.5" backspace gave me 1" of clearance to the springs on the inside.
The tires on these have an 11" section width with a 9.5" tread on a 9.5" wheel.
5.5 is what I am ordering rather than trying to push the limit with a 6" back space not knowing if a wider tread tire may have more section width.