For me HW50 will not be too bright. At the moment I have 2.7 m wide screen and planning to go to 3.1 m. For me the brightness is perfect.
(Gain 1.0) Here in Germany most guys have normal matte white screens with Gain 1.
And most not wider than 2.5 m. Many do have only 2 m or even smaller. With about 800 lumens in low lamp mode you get about 33 fL on a 2 m wide Gain 1 screen. For me this would be way too bright. Also black level would not be very good.
Yes you can use a ND-Filter, but for 3D you should take it off manually unless you build a build a motorized sled for it...
You can still use dynamic iris, if you lower contrast control to desired light output preserving most of the on-off
Contrast control affects only white AFAIK, so black level will stay the same so you reduce on/off CR also.
I had a JVC X30 and was used to the good native CR and the manual iris with which you can adjust brightness AND black level.
But I didn't like the 3D (even with the Optoma Glasses) and I do see flashes similar to RBE with the JVCs. That was distracting and annoying for me.
With the HW50 I didn't see these flashes and I like the motionflow and the 3D. What I'll miss is the better lens and the motorized lens with lensmemory.
The VW95 would have been the perfect projector for me if it would be cheaper and much brighter!