I tackled this same project about 4 years ago myself. I bought 20 of these Panasonic WM61A mic capsules also from Digi-Key.
I sorted and tested the capsules to find closest matched pairs for stereo left and right channel binaural mic'ing use.
If you do a searh on WM61A you will find there are published modifications for these capsules where by you can lower the sensitivity of the WM61A for use at Louder Concert recording environments. The original WM61A capsules are very high sensitivity and sound really really good to excellent. But they are prone to overloading due to their high sensitivity.
The modification of the capsule requires delicately separating by cutting a tab on the back of the mic capsule and then rewiring your external battery box circuit to rearrange the configuration of the FET circuit such that it is less sensitive. They claim improved frequency response changes too, but I think that is subjective. I made a stereo set of mics with unmodified capsules built into a cheap set of Sony headphones and I also made a set with the modified mic capsules. They both sound really good.
The unmodified capsules sound brighter (more high frequencies emphasis) than the modified capsules. The modified capsules are much less sensitive than the unmodified capsules and also have duller high frequencies response. They both sound great and make excellent recordings.
Also beware that when making the Linkwitz modification (as I think it was called) that there are two ways to wire up the DC power supply voltage to the FET circuit. The two different circuit layouts accomplish basically the same thing, however, one circuit has the DC polarity of the supply reversed such that if you do it that way, then you will also have to make sure you have a reversed battery box to supply the voltage to the mics. The other circuit was added later that I could tell and does not require you to rewire your battery box (in other words its polarity is correct and compatible with original standard battery boxes). Anyway, that's all I have to say on these capsules. They are great sounding capsules and can hold their own with the more expensive lavalier type mics. Really!