Get the X3200W. You won't notice the difference in power. It takes double the wattage from a receiver to achieve +3db more volume output. It takes +10db for a perceived doubling in volume to our ears, with +1db being one of the smallest increments we can tell the difference. So the slight difference in output from the X4200W is negligible.
Now, there is a potential SQ benefit. The X4200W has Audyssey XT32 with SUB EQ HT. That room correction can improve the sound a bit over the XT version in the X3200W, and would be a benefit if you ever go to dual subs.