Depends really on how high you want to overclock if indeed at all, the performance between them won't be hugely different. The Noctua NH-D14 is widely regarded as the best aircooler, but it is large and pricey. The Silver Arrow is much more affordable and would be fine medium to high overclocks depending on the CPU. I don't know a huge amount aboout the Fenrir but I can't see its performance beating the Silver arrow, let alone the Noctua. I'd suggest reading a few reviews from a decent review site.
If you can't find a stockist for the Silver Arrow, just get the Thermalright IFX-14 and some fans, they are practically the same.