Yeah, these are some great shots!
Aaron, I like that you're explaining what you're doing so others can learn how you're achieving the shot...This is how they'll learn
Dont get me wrong, I dont mind using the flash, and you'll see it on my camera with a Sto-Fen Diffuser 90% of the time while I'm shooting portraits, but I still like to try and use natural light if it's available.While I agree in shooting in full shade and on overcast days are best - there is no reason to fear the flash. There are many cheap or even free flash tricks to make the flash seem more natural. The proper use of flash allows you to get those eyes bright and clear as mentioned above. Once you are comfortable with the flash you can use it to fill flash and help balance the subject vs the background.
One of my favorite tools is simply a reflector. I have one that has silver on one side and gold on the other. My wife is always with me on all our shoots as both a 2nd shooter and this was we can assist for one another.
Having her hold the reflector and help bounce some light up under the eyes or into the shadows of the model can make or break a shot.
This was a recent shoot we did where I had the model sit under a big tree in the shade. My wife stood about 20 feet behind us out in the sun and bounced some light off the silver side of the reflector onto the model to bring out the shadows
This one she did the same thing, but used the gold side which really warms the model up and gives it a different look
This light reflector only cost $20 and it folds up small enough that it always stays in the truck behind the back seat. Heck, almost everyone here probably has one of the silver reflectors they put in their windshield to block out the sunlight. I've used that before too in a pinch