Yeah, I tried a 5" LR and 6" other tires. Did not find an advantage, although I also did not get to experiment with this package much either.
I originally hoped that the 5" tire would have a softer spring rate, due to its taller sidewalls. But a quick check on my tire spring rate tester indicated that my 5" tire actually had a slightly harder spring rate than my 6" LR tires. (Many factors could be in play here - my 5" tire is older than my 6" tires, and it has a harder rubber compound than what Maxxis is offering now. All of my left side tires, including the 5", are Maxxis "Blue" due to track rules.) I have not prepped this tire at all yet - just cleaned it with Go-Jo.
Since the 5" tire was harder, I held it out to only use if the track had gotten really hard. However, due to weather conditions effecting the track and due to running only a limited schedule, I only ended up racing it a couple of times. My "feel" was that the 5" was a little too hard, but my overall lap times and race results were about the same as usual.
Also note that I ran this tire on a 1999 Undertaker chassis, which is still a good kart but no longer up-to-date with the newer stuff. I was in the box stock Predator class, so engine power is also a factor here.