I think I might be able to help you out some. I listened to the Pio 1120 and 1522 (rebaged SC 65 I believe), Denon 4311 and X4000. Onkyo 818, and Sony 5800es. I had all the AVRs hooked up to the same speakers in the same room for two weeks at a time. My decision works in my room (Great Room opening up to Kitchen and three bedrooms over 12,000 cu. ft.). I run Energy C-9s a CC-3, dipole surrounds, and Infinity highs (I know speakers aren't all the same, but the front stage is). Two Klipsch RW 12ds (not the best, but has to do for now). I also use a Emotiva XPA-1 (but also listened with only the AVRs). In the end, I kept the 5800es over all the other AVRs.
Room correction (ease and accuracy) leaned toward the 5800. I used the Onkyo 818 (Audyssey XT 32) the longest (what was in my Great room for more than a year), but it seemed to over exaggerate the bass (sounded muddy in the lower end). The Denons had the same Audyssey XT 32, which gave me the same lower end muddiness. The Pioneer (MCCAC) had nice airy highs, but the lower end wasn't there (I did read the MCACC thread about boosting up the levels). The 5800 had the separation in the highs, and integrated the lower end (especially my two subwoofers) the best.
How many speakers are you planning to run? I chose the 5800 over the 5700 because it was 9.2, with outputs. I think the 5700 is about the same, sans 7.2 (but you can get 9.2 with an external amp). If you like to listen to movies/music loud, you should seriously think about hooking up an external amp. Cranked up, the 5800 did seem to struggle. Like I stated before, the 5800's room correction was a breeze to use. Just place it on a boom at the main listening position and in about 3-5 minutes it's done. You can go in and tweak settings afterward to your liking. Everything was spot on (distance wise) after running it five times. This was a God send when it came to the wife and family.
There is no upscaling to 1080p over HDMI. It does upscale Component (RBG or Yellow) to 1080p. All the other AVRs upscaled HDMI signals (but it lead to longer switching times and handshaking issues). Personally, I like to run things native. I really don't miss anything the Onkyo, Denon, or Pio did. I do use a Darbee, however, and this may be the reason things don't look different to me. Switching between devices are fast and no green screens.
There is also a ethernet hub built in. One line coming in from your Router and you can hook up to three other devices to the AVR. You can use the Automated system (dimming lights, home security, etc.), but you have to pay $300 to unlock it and have it hooked up professionally. Internet works fast and flawlessly. I do stream music (Sony's Unlimited), and never had any buffering problems.
I guess that's about it. I'm by no means an Audiophile, but "to my ears" the 5800 sounded and worked the best. You should really do what I did. Bring home all the AVRs (you are seriously thinking of getting), and run them for a couple of weeks (same speakers, same locations, listening environment unmolested). I did talk to managers/supervisors before ordering, letting them know of my intentions. If they weren't cool with me sending the AVRs back, I went to another vendor. Heck, I even ended up keeping a "Like New" from Amazon (fantastic price and same warranty). Which reminds me, Sony gives you a five year warranty. What that really means, I don't know. Let me know if you have any more questions, and I'll try my best to answer them.
Good Luck! And have fun!
p.s. Some will get into the reliability of Onkyos. I've had four Onkyo AVRs spanning over seven years. One went to my brother, another went to my Mother In Law, and I still have the 818 and 809 running in bedrooms. They are all working, and never once had a hiccup.
The X4000 blew the amp board as soon as I hit the power button. My Pio 1120 sub out put detached (no longer any bass frequencies out put to the sub) after two years. Just the luck of the draw. Knocking on wood the Sony lasts.