I’d say it would depend what your progress is residing at in current training block/focus.
If you’re targeting SS to say 60 min interval and you’re currently able to ride 50 min continuously it would probably make sense to bump power requirement and progress interval length again at new power.
At least that’s the progress method I’m going for currently.
SS 60 min, TH 40 min, repeatable <3 min and amp up the power (because it’s fun) since I don’t have any events other than training and hopefully a football comeback.
I had the exact same question and Nate said what I suspected:
“If you’re inexperienced and still newish to structured training I would go for the higher FTP.
If you’re like 4.5 watt/kg and going to be a TTer then I would stick with the old FTP and go farther through your PLs.”
I would up levels. I have a similar PL distribution to you (low Thresh, high SS Vo2) and notice that Vo2 around 6 PL still should be very achievable with a new FTP. eg Hillers 4x4 at 111% when the old 8 min FTP test used to be 2x8 at 111%. Also threshold intervals at that low level really aren’t real threshold intervals that one would recognise as such (e.g., not close to the historic gold standard of 2x20 @ 100%)