Hi incognito1, I'm an italian pipe smoker like you and love Samuel Gawith Virginia Flake.
IMHO the strenght of Gawith's EM-type Tobacco could be 18ml, but for example all Dunhill EMs (965 Mixture, Standard, Nightcap, Early Morning) can be a little stronger nico, around 20 to 24ml.
For Rattray's Highlands Targe, it could be again 18ml...for Timm 1000 nico MUST be 24ml (that means the stronger tobacco taste, the lower nico percent).
Hope this IMHO message can help you and the others.
Ciao ciao from Genoa, Italy