The Corsair H50 is crap and easily beaten by the best air coolers, the Silver Arrow trades blows with the Noctua NH D14. The H70 is a different story, but I think I would still prefer to have the Silver Arrow. Especially considering the price, even if the H70 outperforms the Silver Arrow (unlikely), it is not going to be worth the £20 price difference.
If you can get the Asus P6X58D-E for cheaper (significantly) than the Premium you should, unless the Premium has a feature you know you will need.
Is there a particular reason you specifically want a Tagan PipeRock? I ask as I'm not that familiar with them, and want to learn more.
What case are you using?
Have you checked out overclockers.co.uk? Sometimes they do good deals on components.