I don't think changing your pick is going to suddenly start shaking the room; I'd look elsewhere in your signal chain. But if you really want to get geeky, apparently in his Revenge days he sometimes used .96mm nylon Dunlops.
The gauges on the Shergold site don't match the gauges he gave in Bass Player, so either one of those sources is wrong or he's using heavier strings these days. 
The same article quotes him as using Elite Bass Sensors, which don't seem to exist.
I imagine he pays less attention to these things than we do.
#1 might be answered with another question - why did the Eccleshalls ever have a neck pickup in the first place? His other basses don't have one. (For that matter, why don't they just have a pickup in the sweetspot?)
I don't blame him for not wanting to drag the Shergold onstage, that thing's a beast. You'd have to shave an inch off the neck, too. Why not get someone to build a custom 6-string light enough to use live? A 6-string Eccleshall?
As for the Clone Theory, when did he stop using them?