The two conductors take similar tempi in most of the movements (the main difference being in "Venus," where Dutoit is noticeably slower, but I did not find that to make as big a difference in my enjoyment of the movement as I thought it might when I read the timings. Both versions have their virtues, although neither matches Karajan for sheer beauty) and the sound quality of both recordings is exemplary. The RCA (engineered by Tony Faulkner using "24-bit technology" [which we will assume refers to the technical specs, not the cost]) is slightly warmer and more distant in sound than the London recording (engineered by John Dunkerley with, presumably, 16-bit equipment), but the difference is not a great one. Both recordings, by the way, do especially well by the organ pedals, and will give subwoofer owners reason to smile.
So what can I really say? The Dutoit has held off all challengers for more than a decade now. To mention just a few of the major contenders, the EMI Previn has that slight touch of distortion that I was never able to completely listen around either on LP or CD (but others rave about--to each his or her own, I guess), the Telarc Previn is tremendous in terms of sound quality but the performance is a bit bland, the DGG Levine/Chicago reading had its exciting moments but was a bit too sloppy overall, and the DGG Gardiner just sounded too bright to these ears.
The Slatkin is the first recording/performance combination to equal the Dutoit overall in my experience. I very slightly prefer the sound of the Slatkin, but I also very slightly prefer the vocal sonority of the women's choir on the Dutoit in the last movement to the children's choir on the Slatkin.
Overall, then, I have a slight preference for the Dutoit in terms of performance, and a very slight preference for the Slatkin in terms of sound quality, but hasten to point out that both are very, very good in both respects. That the Slatkin recording contains an extra selection, Arcana, does not enter into the calculation--it is a piece that you might want to listen to every once in a while, but I'm confident that most purchasers of this disk will generally skip right over it and go straight off into space.