Hi MN Chris,
A number of ways we can look at your question concerning 30/30 at vVO2max versus the more traditional 800-1200 repeats at the same pace.
Purely logically, we can say that if you find the 30/30s to be a breeze, yet struggle on the 1200s, then the 30/30s cannot be doing their job, because both of these sessions are meant to be exercising/stressing the same thing. If they are both stressing the same system, then it should not matter (within a couple of percentage points) which exercise you do. Once you have got fit doing one, you should be able to do the other. I am confident that if you could do the 1200s, then the 30/30s would be cake... but not vice versa. Which makes you think, no?
Or we could look at the work Astrand and Rodahl did way back in 1970 and discussed in their magnum opus Textbook of Work Physiology. Since it is on the shelf behind me, let's look at it. They discuss (p398 of second edition) their study of a cyclist who was set a workload he could maintain for 9 mins all-out only. His VO2 at this effort was 4.6 L/min. They then had him try a number of intermittent sessions at this pace and measured his corresponding VO2.
Work time/rest time ? VO2 required L/min
30s/30s ? 2.9 L/min
60s/60s ? 2.93
2mins/2mins ? 4.40
3mins/3mins ? 4.6
So, for this cyclist to achieve the VO2 of a 9 min all-out effort, he had to exercise for something more than 2mins. (Traditionally, runners tend to take this as 800-1000's at 3-5km race pace)
One conclusion the authors made was "for the purposes of taxing the oxygen-transporting organs maximally, work periods of a few minutes' duration represent an effective type of work."
So, to refer to your question, this shows that 30/30 at a pace you can hold for 9 mins is not having the same effect as 3min/3min at the same pace.
However, they go on to discuss a study by Christensen, Hedman and Saltin (1960) of intermittent treadmill running using shorter work periods. In this, one subject was able to run at a very high VO2 of 5.6 L/min when he ran for 10s followed by a 5sec pause. He kept this up for 30 mins (on and off a treadmill ? 20 mins total running, 10 mins total rec) "without undue fatigue and with a low blood lactic acid concentration. At the end of the running period, the load on the oxygen-transporting system was maximal."
If the recovery was increased to 10secs, (10 on/10 off) the VO2 dropped. If the work/rest was increased to 15/15, the VO2 dropped, and as already shown 30/30 doesn't work either...
Note here that the athlete could only maintain this pace for 4 mins all-out (not 9 mins as above), so this is above vVO2max and more like best one mile pace (or faster; the athlete managed 1300m in 4.0 mins). They do make the case that the speed here is critical. For this runner, the pace at 22.75 km/hr enabled his VO2 to reach max at 10s/5s. But if the speed was reduced to 22 km/hr, then he only required 90% VO2max at 10s/5s, but he could go longer (60mins vs 25 mins).
So, "work from a few seconds to several minutes and up to hours of continuous running has been shown to put a major load on the oxygen-transport system, provided the work load is sufficiently high." (note the final caveat).
I tend to use 800s and 1200s as I've shown. We have tried the 30/30s, but everyone finds them too easy (can run all day and do not reach max). I have not ever tried the 10 on/5 off at best 4.00 min pace. And have never heard of good athletes who have done so (anyone used this?). It might be interesting...
One final point. Cardiac output and stroke volume attain their highest values at a load which produces VO2max. Training above this pace (ie: faster) the oxygen uptake, the cardiac output and the stroke volume may actually drop. To close with a quote from Astrand and Rodahl, "there is no evidence to support the assumption that it is important to engage the anaerobic process to any extreme degree in order to train the aerobic power." (p404).
Meaning there is no need to reach a state of "knee-grabbing" or reaching exhaustion, yet still be doing the optimal (aerobic power/aerobic capacity) training possible.
Final thought: in an earlier thread (to CBASS), I stated that if your aerobic ability is not good, you will not manage these 1200s. Above, you yourself are considering the same thing...