You might get away with it when the lamp is newer. Also if you are nearer the short throw end of the projector (so applying more zoom) then the image tends to be brighter. For example my current HD350 is at minimum zoom long throw so my iris is opened up a little over half, in normal lamp (the higher of the two settings) but my screen is 1.5 gain and slightly narrower than yours at 112" plus I have a lens. I can hit 12-14fL even after 200 hours on the new lamp (first one dimmed a bit after 700 hours), a shortest throw setup may well add upto 40% more brightness for comparison.
It depends on taste but you might find you're happy with less than I'm currently getting, plus it is possible that the X70/RS55 is brighter after calibration than my HD350 (even if they both had new lamps), so you may have more in hand than me.
"Don't believe everything you read on the internet". William Shakespeare 1615