With prices of £158 and £166 respectively, the Corsair AX760i and AX860i are more expensive than the power supplies from our recent round-up, but you do get high-quality PSUs for that price. Their efficiency is outstanding, they're extremely quiet and the voltages are super-stable.
Slow computer got you down? Maybe a hardware upgrade should be in your cards, if so this guide to the Fundamentals of Upgrading a PC is an invaluable read. PCSTATS Tips