If you received an early BENQ XL2720Z unit with V1 firmware, there is a behavior in BENQ Blur Reduction where the strobe backlight flashes too early in the LCD scan-out.
UPDATE: This was done to decrease input lag by ~1-2ms with worse image quality. Fortunately, this becomes a user choice in V2 firmware with the Blur Busters Strobe Utility.
This will cause double-image effects in the bottom 1/3 of the screen during panning/strafing/turning motion (such as www.testufo.com/photo) . The good news is I have told BENQ about this, and BENQ is making this adjustable for subsequent shipments of XL2720Z (with a utility), and via a V2 firmware upgrade.
Another good test is the TestUFO Alien Invasion Test using Height -> Full Screen. Ideally, there should be minimum crosstalk/minimum ghosting for both top and bottom edges. However, the XL2720Z has a major double-image effect 2/3rds of the way down on the screen, when Blur Reduction is enabled. See new illustrated photograph (different one).