I am aware that I am looking to strings to solve a technique issue, and that the real answer is practicing more, however- for those of y'all that have experience with both, how do Flexocores compare with Spiros in terms of buzz/growl/mwah on stopped notes (pizz) and power? I'd like to retain the power of my Spiro A, but when playing bluegrass in B flat or B when it comes time to really mash the one I'm getting a bit too much buzz.
Although virtually any string can be used for pizzicato, all varieties of Flexocor are meant primarily for arco.
And, I think "buzz" and "growl/mwah" are two different things. "Buzz" indicates a need for fingerboard maintenance, while "growl/mwah" are typical of some strings that don't have much damping. Flexocors have a fair amount of damping. But, as @KUNGfuSHERIFF says, the Flexocor Deluxe seem to have the least damping among the Flexocor varieties.