I can't speak for the other receivers you have listed, but I purchased the X4000 a few months ago and have been very happy with it. I ended up paying about $1000 for an open box unit at Best Buy, it is going to be difficult to find the 4520 or the Marantz within your budget. I purchased a Pioneer SC-67 prior and returned it and ended up with the Denon shortly after.
I like the X4000 for several reasons:
-Plenty of power and the sound was an upgrade from my previous receiver
-Matrix switching from the Zone 2 HDMI output, any source can be played from Zone 2 independent of the main zone. This was a big one for me so the living room and media room could share sources without interference or having to share a source. It also saved me from having to purchase a switch.
-Dual sub outputs with EQ from Audyssey