With the i5 vs i7 it really comes down to if youll make use of the hyperthread. Many will not, and most gamers will not.
But, Folding at Home (cpu based), Video encoding etc are some things that can take advatage of it.
Some games do aswell, but very very few. The games that do are pretty much limited to RTS games such as Total War and Civ5 as examples. Most 3D action, shooter, adventure games will not make use of the HT.
And Corsair are good PSUs. Many are rebranded Seasonics, such as the AX series. Regardless, they are quality Power Supplies.
Seasonic, Corsair and Antec are my personal recommendations for a PSU.