I heard the Sony X and it's performance is pretty poor. Best Sony DAP I've heard but it doesn't say much, Sony's brand name is usually associated with good sound but I don't think that's the case with their DAPs quite yet or anytime soon. The 845 is even worse from what I've gotten from other users I know here.
RMMA are good indicators, just that most don't know how to interpret the results. It shows the cold fact, there's an apprarent output issue with that Sony and it's going to roll-off those sensitive BAs no matter what. If there's a poor stereo crosstalk result, it's going to be less open, etc. The Clip+ only graphs really well with sensitive BAs, otherwise it's performance is average and nothing special (though solid). The Iphone4 you have there graphs really well, I heard it myself and it's pretty amazing. It may replace both of my DAPs if it ain't broke, don't fix.