Opto,
You want to run a pace that you can handle. The purpose of the workout is to learn the pace, gain confidence in yourself by demonstrating to yourself that you have just a little more in the tank to bring it home in style.
So what is the right amount of rest?
Measure your HR and rest until you get into 90 -110 bmp (moving towards higher as you progress). If you have done enough long runs, that should be about 3 min and your plan sounds fine. Chances are that you achieved your PR's in cooler weather and the pace you have listed is a bit of a push.
There is one approach I would suggest. Pace down a little (46-48) and then do another similar workout in 3 days at target pace.
Mentally, you should evaluate form not effort throughout each run. As you tire out, think about what you are defaulting to doing under those conditions. Monitor those things. Do you whip your head back, pin your shoulders back, drop your hips, look more or less like a pregnant lady running after her toddler?
Your workout should not be about hustle but about confidence.