Some more dynamic iris discussion
So, it will really come down to whether to save a few hundred dollars, by giving up a little here or there. Basically, you will get a bit better blacks. Shadow detail is also at least as good as the 6500UB, and actually looks a little better in several of the images. In addition you get improved CFI, and the new Super-Resolution, which has some merits. So, if you are a "performance" oriented buyer, it comes down to a really good projector, or one that is essentially the same, but better still. Spend more, get more. You'll have to decide how much more the Home Cinema 8500UB is worth to you, at least for the few weeks they will overlap each other.
I need to point this out - a doubling of contrast should provide a small, but recognizable improvement in black levels. Thus, you should see about the same improvement going from 2500:1 to 5000:1, as from 30,000:1 to 60,000:1.
In this case the Epson jumps from last year's 75,000:1 to 200,000:1, which is also, a small improvement.
More to the point, the bulk of the improvement comes from a new dual layer dynamic iris. That means (per Epson), that it can generate blacker blacks, and that we're seeing. That doesn't mean, however that blacks improve significantly in scenes where the iris is completely ineffective (bright scenes with dark areas), or partially effective (scenes where almost no areas are above 50% brightness). This is true of any iris operation. With a dynamic iris to darken blacks it also needs to darken whites and everything in between. According to Epson's provided technical description of the new iris, there should be some improvement in blacks in most scenes, but in those mid-brightness scenes, any improvement is extremely slight, compared to darker scenes.