Well.... I had the 5308 when I bought the 4310 for a second system.
I decided to try the 4310 out in my dedicated 2 channel system, where a NAD dual mono block amp resides. The 4310 did an outstanding job of driving my VMPS RM-40's, monstorus 7 driver, 4 ohm, tough to drive speakers.
The 4310 did such a great job with them that I decided to try it out in my main HT system where the 5308 has resided for the past year or so. I wanted to compare the video processing of the 4310 to the excellent video of the 5308. The ABT video processing was up to the challenge equaling the 5308's in my opinion. In fact the 4310 did such a good job replacing my 5308 that I decided to sell the 5308, got nearly what I paid for it, and use the 4310 until the 4810 becomes available at a decent price.
I've recently gotten into Audyssey DSX (wide) and love it but I don't like giving up 7.1 and all that comes with it DPLIIx, HD 7.1 codecs, etc...
So my next receiver or processor will have to be 9.1 at least