Mixing regular interval training with HIIT - too much?

You are only supposed to do HIIT 3x a week max. However, does this apply to all forms of interval training or just HIIT? The reason I ask is this..

Recently I changed my routine. Four times a week I will do some sort of resistance training (lifting with free weights or body-weight exercises). After each session I will do some form of cardio. On two of the days, I will do HIIT afterward. On the other two, I will do 30 minutes of SS cardio afterward (30 minute treadmill walks). On one of my SS cardio days, I decided to do an interval style routine instead where I mixed 2 minute intervals of  power-walking @ 4.8 mph with 2 minute intervals of slow walking @ 3.0 mph for a total of 30 minutes (3 minute warm up, 22 minutes of intervals, and 5 minutes of cool down). During the power-walking sections, my HR got up to 180 (93% of my MHR) because I was doing two minute intervals @ such a fast speed for walking. It turned out to be a great workout, and I felt very good afterward. It was so much better than regular walking.

I would like to do HIIT 2x a week, and change my two SS days to interval walking instead. However since I get my HR up to 93% during the power-walking intervals, would this be like doing HIIT 4x a week? I figure that since I am getting three days off a week, I don't run the risk of over-training. However, doing HIIT 4x a week is too much. So if what I did was a form of HIIT, what level should your heart rate be @ to make the workout classify as regular interval training instead of HIIT? Or should you only do any form of interval training 3x a week?

Actually, that's 2xweekly on a regular basis, otherwise performance suffers.

 On a 3xweekly schedule of intervals, compared to a training program made up of steady state sessions of comparable training loads relative to your maximal performance you'll notice the following:

Weeks 1-3: Interval training gives faster results, and you are consistently achieving better times and a higher VoMax than the trainee doing steady state.

Weeks 3-6: your results are beginning to stall, your performance is not improving; while the steady state trainee continues to improve. Your overall performance is about equal.

Weeks 7+: Your performance is starting to degrade from overtraining syndrome and too much training at too high intensity for too long without a break. The steady state trainee will continue to improve performance. On all performance parameters and test scores he's completely trashing you.

 Overall, only the first 3-4 weeks of an interval program with that training density gave you a noticeable performance boost at first, at week 6 or so your performance metrics will be about the same training either intervals or steady state; and from week 6 on out your performance will be noticeably worse and will keep on degrading compared to that of a steady state trainee.

 For fat loss intervals are unrivaled by anything save strength training - strength training+diet thrashes any other training method for fat loss purposes, but performance-wise intervals are of strictly limited utility and it's not a case of the more the merrier.

 The optimal use of intervals for performance is to build a broad base using mostly steady state and sharply limited blocks of 3-4 weeks of intervals to peak your shape and performance starting approximately 4-5 weeks before the event you're training for.

 Obviously, this only applies to people who give a damn about endurance performance metrics, I personally couldn't care less about my endurance performance - but you'll notice that the performance degradation from too much high intensity work applies to all CNS-intensive activities, including maximal-effort strength training. And that I do care about, very much so.

 Intervals are much like plyometrics* - a valuable tool in the toolbox, but overused by idiot coaches who don't know when to stop.

Olympic athletes will do intervals of all kinds a maximum of 2xweekly on a regular basis; anything more sacrifices long-term progress in the interest of short-term results.

 You know, I am not now, nor have I ever been aware of the meaning of the word restraint - but a little judicious planning for where you're going to expend the majority of your effort and what performance metrics you're planning on improving doesn't hurt. It's not physically possible to get better at every performance metric at once because the physical adaptations that improve performance in one part of the fitness continuum competes with or blocks the adaptations for the other parts. You can put your own personal goal dot into that performance spectrum or figure out what the optimal blend for any given sport is and let that decide where you're focusing the majority of your efforts. 

 But if you try improving everything at once you'll just overload the system and get nowhere - you need to pick one major and two minor goals and construct workouts around them to apply a useful training stimuli that moves your body in the direction you want to go. Push on it from all sides at once, and you're going nowhere fast.

(*Plyometrics should only be applied in 4-week blocks once every quarter, more is just begging for a joint injury. And you should be limited to 40-50 ground contacts per session if you're doing 3xweekly, 50-70 if you're doing 2xweekly; there are morons out there who have you doing plyometrics with a couple hundred ground contacts per session 4xweekly for 3 months at a time if you follow their program as written. IMAO they should be taken out and shot, that's just a recipe for persistent overuse injuries and stress fractures. )