the heat range is the self cleaning temperature a plug has - it is determined on how deep is the cavity between the center electrode and the shell. The deeper the cavity the higher heat range a plug has because heat will take some time to dissipate into the shell if its farther away,
Installing a plug with too hot a heat range on a high compression engine can induce knocking as the mixture compresses and is faced by an already hot plug which starts to glow in the compressed heat firing it off before spark. But installing a plug too cold will take away the self cleaning charecteristics of a spark plug and result in fouled black plugs. Hence you need exact heat range plugs as your manufacturer recommends.
About 4 tips giving you good power and all, ITS ALL IN YOUR HEAD because the shop keeper told you so - or your previous plugs were so badly worn out that you had lost nearly all engine power. Multielectrode plugs are only good when you have a big brute of an ignition coil (not your choohia ignition coil)