Which plugs are best for performance?

Allways!
Best plug is the fastest plug!
(Next guy)
NO! Best plug is longest lasting!
(Next guy)
NO! Best plug is....

As far as heat range goes, stock to 1 cooler for most Street and street strip rides. Track testing (or dyno) will show what's fastest and regular driving should be tested as well.

Most cars will not go 3 steps cooler.
Race rides... well... what ever works best. When the times go down, your doing it right.