I Own 2 Extra Hollow Grinds..They are Wicked Sharp & the Blades Can Flex with Undue Pressure..You are Unlikely to Find an Extra Hollow 4/8th..As I Said..They are Rare..Some Full Hollow Grinds are Almost as Thin as Some Extra Full Hollow Grinds..
Full Hollow Grinds are Fine for Anybody..An Extra Full Hollow Grind can Cut You're Face to Ribbons in Jig Time..My Henckels Friodur Full Hollow is the Same..They have Paper Thin like Blade & Wicked to Use Even to the Experienced User..I Personally Wouldn't Recommend them to Beginners..
I Got a Russian 5/8th from this Seller NOS..He Does 4/8th as Well..They are Great SRs..Mine Honed Up Very Well & Took a Killer Sharp Edge..
http://www.google.co.uk/aclk?sa=l&a...ahUKEwjOmZbgkrXQAhXJK8AKHUc2Dq8QvhcIIg&adurl=
Billy