Plugs should be NGK BR9ECM.

Does the bike pull through the redline in lower gears, say 1st, 2nd, and 3rd, or does it "fall flat" at around 8000rpm which in 6th is about 120kmh?

Failing to pull through the 7-8000rpm barrier would indicate an RC Valve failure - either something in the PGM or something mechanical has broken. (Maybe a cable, or a/both Valve(s) "gummed" up.)

Andy.
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