Well, "softer" and "firmer" are too simple to describe the differences.
BT7 lost the "dynamic" nature of gut resilience, IMHO.
Try stringing Wilson gut(original VS) somewhat tighter and compare them.
You'll feel the dynamic nature of it. Bt7 also loses resilience much quicker than original VS. BT7 therefore feels and performs like synthetic multis to me. I experimented with it for 1 year and I'll never use BT7 again.
Question is, will babolat change formula for Wilson eventually or not? Should I stock up large number of Wilson gut now or not?