Without testing it can be done after the fact using % of vo2 max from Power Curve ( simple equation:
ewma((power*0.0108+metric(weight)*0.007),25)/(athleterange(date-89,date,vo2max(meanmax(power)))) )
But I do not know how to check it outside wko - probably it can be done in intervals.icu by someone smarter than me as I didn’t play with coding in intervals.icu.(will start as it’s an awesome platform).
But when it comes to power while doing vo2 max - just go submaximally 
If your 5 min power is 355 almost by definition you can’t use it as your vo2 max power for intervals as this is maximal effort. Given that you have no problem doing 5x5@320W as repeatable power, your 5 min MAX can be even higher.
The best verification for vo2 max is your feel on the bike - if you are gasping for air and breathing like a fish out of water it’s all good. Even if the power is decreasing during subsequent intervals but breathing is there - you are getting good stimulus for the adaptations.