I have hunted rattlesnake infested country for 50+ years and have a healthy respect for them. Currently hunt an area with knee to waist high grass and lots of large rattlers. Most rattlers I have seen are not aggressive (have only seen two that were).
I always wear snake boots in the event I cross paths with #3 aggressive rattler or simply step on one I did not see in the tall grass. While I have my doubts that every snake would strike below the boot tops (16" IIRC), the boots offer some degree of protection. I have used leggings in the past, but found that I will wear the boots as they are the only suitable footwear I have with me. I did not always put the leggings on over my regular hunting boots.
You might want to look at the snake chaps Cabelas offer. They are very easy to put on (snap onto your belt), probably cooler than leggings, and come clear to the waist. Only drawback I have found on the chaps is they are a bit noisy in thorn brush as they are nylon.
One tip on the snake boots, be sure to get a pair w/goretex lining for comfort. Unlined snake boots are very hot in warm weather.
Regards,
hps