First came accross Pirastro Obligato strings when I discovered Dan Bergalund, (e.s.t. bassist) used them. Although they don't quite have the sustain or 'zing' of Spirocores, they have a lovely depth of tone and do sustain well, especially in the lower registers. They demand more 'flesh' across the strings from the fingers, but when use to playing them, they really growl when playing pizz style. They have a good arco response. Any others of you use Obligatos?