Thanks for that jake. I'm going to closely compare the string in the photo to mine. I've ended up buying a spirocore A to put with some used spirocore d & g, and a superflex e. I'm worried about the bowing, as I'm still on Simandl and working on PC tunes. If the wonder tone is synthetic core that's a whole step away from steel rope core! I always strung my violins with dominants and the occasional olive, but on the bass I can't afford it just now. At the moment I'm thinking I need spiros and a schertler basik and a second hand GK to just get a good entry level sound.
I'd buy your extended E if I could get hold of a fawcett or slide extender cheap enough. I like the idea of shifting the extender to C,D,Eb etc for practicality, but also for the open harmonics and bigger bass.
Anyway thanks, I'll read about wonder tone, and see how the spiros go, especially with the bow!