One more thing. A good rule of thumb I use when coaching people is when doing VO2 Max intervals (I pace) is to run half the distance of the interval in less than the time it took to do the fast part. In your case that would be 300 meters in less than 1:55. In your case you were doing 200 meters in 1:30 to 1:45. A 1:30 200 is 12:00 pace, and a 1:45 would be 14:00 pace. It's no wonder you were able to run so fast for the 600's. If you are truely in good enough shape to run your 76 second I pace, then running the 300 rest in about 1:45 shouldn't be too hard. I always tell people that if the I pace seems too slow, then they should run the recoveries a bit faster, or go longer for the I paced intervals.
It's fine to take long leasurely rests for reps. I generally use twice the distance covered in the rep for the rest. This would take about 3 times as long as the rep time wise. I believe Daniels recommends 4 times, but this can make for a very long workout.