...So taking into consideration my own personal experience with a Silver Arrow SB-E and what I've read and listened to concerning the other options I rightly or wrongly conclude the following:-
1) The NH-D-14 is still good but has been bettered and doesn't represent the best value for money.
2) The PH-TC14PE is the possibly the best when dealing with an overclocked CPU but it's fans have an irritating drone and it represents comparitively reasonable value for money.
3) The K2 Mount Doom offers great performance, not the the best, but offers the best value for money.
4) The Silver Arrow SB-E performs well and has the quietest and/or least irritating fans but isn't the best value for money due to it's present increased price.
5) The Silver Arrow SB-E Extreme is possibly as good or better than the PH-TC14PE but it's fans are loud and will probably be more expensive than the standard Silver Arrow SB-E, so it potentially fairs poorly as far as value for money is concerned.
As far as asthetics go take your pick, that is if you care at all. Just consider that with any of these coolers, you won't be able to use RAM with pointlessly large heatsinks and you can almost certainly kiss goodbye to using your uppermost PCI-E slot on your mobo. Also, if you are considering getting different fans for any of these already pricey air coolers, then you might as well dis-regard any of the above comments on value for money.