sprints and recovering

I have this HIIT-like sprint interval training workout that I like to do 2-3x/week... it's only about 20 minutes long and consists of a 3-5 min warm up, then 8-10 all out, full speed sprints. You sprint for 30 seconds and then recover for 60-90 seconds, and then its on to the next sprint... etc. repeat until all sprints are completed, then cool down for a couple minutes.

pretty easy concept right?

well my question is if I am sprinting at 10mph (for 30 seconds) how much should I decrease my speed to for the recovering periods?

usually I do my recovery periods at about 5mph, which is a light jog... is that good enough? or should I increase or decrease the recovery speed?

I know these workouts are all about switching your heart rate and oxygen uptake, so I want to make sure I'm doing it right

Ask 10 people this question and you will get 10 different answers. Depends on your fitness level.

true.. but don't you need to keep your heart rate at certain levels during the sprinting portion and the recovering portion?

will going from 10mph to 5mph be enough of a difference to get the best results?

FYI: I'm 5'2(1/2) and my average running speed is about 6.5-7.0 mph... if that helps to figure out my "fitness level"