Should I run X 2 spark plugs or Metal plug?

In my experience, if the first plug "just goes bad" then the second plug will probably be okay. If the first plug fouls due to a tuning issue for example, the second plug will likely be dead as well. So you never want to rely solely on the second plug in the head as your only spare.

I would not recommend two heat ranges... the spark itself is flea power in terms of heating the center electrode and insulator of the plug. The center electrode and insulator are "tuned" (heat range) to get hot enough to stay somewhat clean, but not too hot so they become incandescent and cause preignition when exposed to the blast furnace of combustion. "Hot" plugs have a longer heat path and "cold" plugs have a shorter heat path. How hot the center electrode and insulator get when exposed to the heat in the combustion chamber is not dependent on if the plug is sparking.

When I was young at the races it was somewhat common to warm up the bike on a "hot" plug and then swap to a "cold" plug for the race. One of the older guys in the neighborhood that was racing decided to run a really hot plug like a B5E or B6E in one plug hole for warm up, and then switch the plug cap over to the B9E or B10E for the race... he holed the piston very quickly after the start. That "hot" warm up plug was the first blistered/melted spark plug I ever saw. The cold plug did not look overheated at all.