Okay I can give a definitive answer on this now
I went to band practice with the little Joyo Bantamp XL Zombie II (through a Laney Ironheart 212 fitted with two Vintage 30 speakers) and two other guitars, one with an Impulse set (in a relatively dark guitar with mahogany set-neck construction and brass saddles) and another with an alnico War Pig set (Gibson SG), all in the same tuning and with the same string set, although the War Pig guitar is 24.75" scale whereas the other two are 25.5" scale.
Of the three the Impulse set Schecter was the brightest, followed by the War Pig SG, with the Cobra Tele definitely being the darkest. The annoying plink was gone, so it obviously was caused by the bridge saddles going out of adjustment when the bridge was converted to string-through. So I decided to desolder the 470k resistor from the bridge pickup lug on the selector switch today and give it another test through the same rig, but minus the clean boost that I had used at practice (I didn't connect the pedalboard, which has the boost). Even without the clean boost the guitar now has considerably more bite and crunch and is on a par with the Impulse guitar with regard to that. In fact it sounds quite epic now.
So I'm calling it: for the Cobra-T use a 550K or 500K pot.
This obviously makes life easier when combined with a neck humbucker. If using a less powerful single coil neck pickup, stick with the 550K pot but experiment with a resistor to see whether you prefer that. With a more high output single coil in the neck (e.g., a P-90) you probably won't.
