most pastes are pretty similar performance wise. especially at the higher efficiency price bracket. tuniq and arctic do 2 of the best (for under 10 bux/7 quid), in the mx4 and silver 5 brands.
pretty much every other brand will be within 1-2'c of these including the corsair branded 1.
delidding wont give you much better temps than you already get, maybe 1'c if your lucky if its an i5/i7 sandy or ivy as they use thermal paste inside the lid not solder like they used to. so its would be a high risk low reward exercise