The most notable upgrades to the Corsair Professional Series HX850 power supply are increased efficiency (80 Plus Gold versus 80 Plus Silver) and the ability to run in silent, fanless mode when the load is 20%. The HX850 PSU delivers very good efficiency with good voltage regulation and clean DC outputs on the all-important primary rails. The HX850 is dead-silent when outputting less than 20% load and under normal operating conditions the power supply is still very quiet."
Any major computer upgrade generally requires a full software reinstall too. No so if you heed the advice in the guide to Upgrading a Motherboard without Reinstalling. PCSTATS Tips