I think you should go the other way with something like Dorr +5. For VO2max work it’s less important what absolute power you are at and more important what physiologic state your muscles are in. You want the muscle to be in a ‘VO2max state’…or past the point where a certain level of oxygen content is in the blood circulating through the muscle. You can achieve that for longer than you think with power levels that are lower than you think.
Do Dorr +5…after the initial high power portion of each VO2max interval adjust power on the fly to keep your heart rate at or over ~93% of HRM. You can rack up many minutes at VO2max if you take this approach. Billat published some whopping long intervals at VO2max in this fashion.
You may have to extend the duration of the first high power start to something more like 90 seconds…but if you don’t want to go to the trouble you’ll get about the same results from the 2nd interval anyhow.