Should I run X 2 spark plugs or Metal plug?

Good point Mark, and I'm glad you mentioned that . . .

Don't be using a hotter spark plug range then what Yamaha originally recommended as being safe for your particular bike.

If your bike is overheating during prolonged hi-speed running with the proper spark plug heat range that Yamaha recommends, then you likely have other tuning problems ... such as ... over advanced timing, too lean on carburetion tuning ... or, perhaps an air leak. For this reason, I recommend that all riders learn how to properly "read" a spark plug ..... especially on these vintage two strokes.

Much more could be said about spark plugs, racing and tuning, but I hope we've covered your basic question. I might add that some have used the second hole to install a compression release, but that was more a thing of the past.