If i remember correctly when i had the black betty i was crossing the line just before limiter in 4th gear, i rarely changed into 5th as i felt that the extra gear change slowed down the times when comparing. My trap speed was 186ish km/h from memory. I noticed on your run you changed very early to 5th. I know many people say there is no peak power after certain revs however in my case i found staying in 4th worked best. Maybe on the odd pass i was just touching limiter in 4th which then required a 5th gear change 30m before the line. Hope this helps, anyways just my two cents.
Solid 60fts mate!
Edit : This was my best time i managed with my betty. Excuse the video quality.
https://www.youtube.com/watch?v=sWslMlWjKSc
https://www.youtube.com/watch?v=kX91SRMNwK4