Often even off a roundabout exiting to dual carriageway may still be in first gear... Maybe it's not optimum like you say, but the way the bike lofts front and powers forward is mind blowing, so really for kicks. (also sounds wonderful)
It all happens so quick tbh, you only have a few options, back off abit and continue to accel in first and ride it out to the limiter... or you can shortshift to 2nd, which keeps front rising and threatens even more silly one wheel antics which at 120+ is getting out of hand. Even if you land the front down in first then shift to 2nd, as soon as it hits power again front is back up in air. (if still bouncing a little 3rd does same)
I dunno, so many ways to ride a litre bike.. only thing I know for sure is most lower gears are strickly for one wheel only when throttle nailed, at least on a modded and geared bike, and if you have managed to keep her down she's shaking head in disapproval as damper struggles to cope with lack of weight on front, sooooooooooooo much fun though.
Need a lot of self control without a doubt, if you think your indestructable, you'll die