Although yes money does buy better quality there does come a point where your throwing money at no noticeable gain. Yes the difference between the worse and best pastes can be as much as 10c but tbh anything thats deemed as a premium paste around the 5 to 15 pound theres very little difference, take a look at the results between mx2 at 7 quid and ic diamond at 14 quid and arctic silver 5 at 9 quid its a little over 1 degree, assuming that those sorts of fluctuations arnt counted as within margin of error.
By all means take a look at that round up and pick the best of the bunch however (and this isnt a dig at stulid i think he did a great job and really enjoy his reviews) reviewing thermal pastes isnt scientific, room temps vary mounting quality varies even load on the cpu when running flat out varies by a small % here or there even when running the same cpu and load programs nothing outside of laboratories is exact and even those tests throw a margin of error %.
Long and short of it is imho most premium pastes in the 8-16 quid bracket will probably perform within 1 and 5 % of one another not enough to really worry about, what i would say is more important is to find a spread you like one you find easy to work with and you know you can get a decent join with, ive always used as5 ive used it for years i know it i like the way it performs could i get an extra degree or 2 by messing about with loads of others, maybe, but tbh im just not that anal and i know when i need it i can always rely on as5 to perform well and spreads easily, ive tried some premium pastes that were lying spreading dry toothpaste, nasty