I find the gel insoles wear faster, and your feet slip around in your boot more. I like the Dr Schools sport insoles.
As for the Mark III boots, they need to be broken in properly. When I first joined, I was fortunate enough to have someone pull me aside and tell me how to do it properly, and I spent an entire weekend breaking both pairs in. Since then, more than 5 years have passed, my boots fit as well as slippers, and I‘ve never had as much as a single blister (touch wood).
And about the "perfect boot" I‘ve learned that no boot is perfect for everyone. Any boot will give someone shin splints or blisters, and everyone likes something different, or has some miracle cure. Make sure yours fit, get them broken in WELL and then just find what‘s comfortable.
Now, to the important part, how to break in Mark III combat boots:
1. Remove all insoles and laces from one pair of boots and place them in the bathtub with the plug in (or a really big pail).
2. Cover the boots completely in boiling hot water and let them sit for several hours, or overnight; until the leather is really soft.
3. Put on your two pairs of socks, remove your boots from the water, add the insoles and laces and lace them on to your feet, nice and tight.
4. Wear the boots until the leather is completely dry (usually takes all day). The leather will harden to the shape of your feet.
5. Apply a thin coat of vinegar to the boots once they‘re dry to prevent salt staining, and then polish them up.
6. Repeat with next pair of boots.
A little effort beforehand will save you a lot of pain in the long run.