Soul is nice, but would be hard to get a particularly good spec on it for £1500 bearing in mind the frame alone is £470.
The Genesis Altitude is about the closest thing out there to a Cotic Soul that exists to be honest (I know, I have one), they are truly excellent bikes! Highly recommended from me, doubt you'd be disappointed.
The Whyte 19 is about the only bike I've seen to tempt me off my Altitude, they are to die for (based on looks alone) I think. The geometry looks a little slacker, and I've not ridden one though, but I'd love a go on one, and the whole bike for £1599 doesn't look too bad value compared to the piss poor frame only price of £649.
456, you can't go wrong, they're great bikes. For your £1500 though you can just get something a bit nicer should you desire. Or a 456 with a killer build!
Carbon 456, well... Never been a fan of carbon for bike frames myself, unless it's a road bike. Strength issues aside (i've seen a load fail, mainly through wear and tear rather than excessive loads) they just remove the rider too much from the trail.
Orange P7, nice but heavy for what it is.
Ragley Blue Pig, very nice looking, not so sure on the mega slack geometry though am yet to ride one and be converted.
All nice bikes to be fair, each different in their own way. Suspect if it's more of an XC bike you're after you'll look at the Soul and the Genesis, possibly the Whyte. More of a hooligan bike then the Blue Pig. And somewhere inbetween sit the P7 and the 456.