I don't really get too concerned about whether something's a speed 6 vs 7, 8, or 9. I just make sure I have the US, stable and OS slots in my bag covered for the following speed categories:
Mid
Fairway
Distance
I understand how flight ratings work, and that they are numeric, but those #'s don't necessarily correlate to specific values that are directly measurable/quantifiable.
Everyone's gonna build their bag as they see fit, but if you're gonna skip over a Leopard because it's a speed 6 rather than a 7, I think you're:
a) doing yourself a disservice
b) reading too much into flight #'s.
Not saying 6's and 9's fly the same.
Just that that you can use range of slightly different speeds to fill your fairway needs. Same for mids and distance drivers.