obx, thanks for correcting what has to be one of the most wrong statements made in this thread.
To add to what you said, here's the reality: nobody in the world knows infection rates where you will be backpacking. That's the short version. The longer version is that, in for example California, they trap ticks and test them, a mere handful, you can look up this data online, they have a database you can access. For example, in the entire South of Monterrey area, they have a handful of sites, almost all, if not all, along the coast, for example Andrew Molera state park, and there they have collected a handful of ticks for sampling. So if you are backpacking in big sur, that data has exactly nothing to do with your actual risk factors.
Also, each eco-region has its own infection rates, so any article that says there is a 1% infection rate without referring to the region/specific area is totally worthless and should be immediately discounted as a valid source of information, since whoever wrote it is clearly totally ignorant and unable to understand the question at hand. Even with regions the infection rates can be totally different depending on specific factors such as presence of walnut trees, ground mice, and deer, to name just one factor.
Because the alleged data is so absurdly and badly done, one group at least in I believe Sonoma/North state counties collected their own tick samples and found up to I believe if memory serves, about 40% lyme infection rates in nymphs.
The other factor is that infection rates seem to vary widely between nymphs (this big: . - and flesh colored, find that in your knee-pit after a hot sweaty day, I challenge you to do that) and adults, the nymphs have much higher infection rates than the adults, sometimes near 50% depending on the area.
The other factor that people need to be aware of is it's very common for ticks to carry up to 3, or even more, diseases, only one of which is tested for, lyme, and that test is extremely poor, up to 50% false negative, which is one reason lyme is such a growing issue in the world, the tests are terrible and were originally not even meant to be used for diagnostic purposes, but were rather intended to test subjects that registered positive for clinical trials, I don't remember the exact details, sorry. So if you are treated for lyme, you may actually have one or two untreated co-infections, at worst case.
Lastly, the notion that using antibiotics as plan A for treatment, that's a very very bad idea, that should be plan B, or even C, avoidance, careful checking (although with nymphs, that's a dream if you think you can spot those each time, 50% of lyme sufferers never even saw or felt the tick, and about 50% never get, or never see, because they weren't looking, the rash), permethrine, should be plans A/B, antibiotic treatment is plan C, and if you don't catch it in time, or don't get the symptoms properly diagnosed (very likely sad to say), look forwards to your backpacking days, and work, and other factors, being over, possibly forever, unless they find some way to get deep seated stuff out of your body.
So yes, use permethrine, it's a no brainer, there is simply no comparison between the correctly noted possible toxic side effects of sprayed clothing and the absolutely certain damage lyme and related diseases will do.
This ignores things like rocky mountain spotted fever, which can be, and is often, fatal.
When talking about ticks and lyme, try to avoid spreading myths and untruths, it's extremely dangerous to have bad information on this subject, just use the permethrine and keep enjoying your hiking, while still being very aware and alert. Or don't, in the end natural selection will take care of the problem I guess, unless you've already had kids...