It's not just plain stiffness, IMHO.
original VS used to be crisp at low impact and surprisingly resilient at high impact.
I used string VS(or Tonic) at very high tension(up to ~68 lb) on 18x20 string enjoying crisp
control on touch shots but still could bring on beast-like power when I take
large cut, exhibiting sweet ball pocketing characteristics.
BT7 lost this dynamic nature, IMHO.