I've found 0.8mm to make much more reliable connections, since the specification says that the tongue should be 0.7mm. 0.6mm will disconnect if the cable is angled in any way.
0.8mm is definitely out of USB 3.0 official spec and might damage the plug. The Spec requires 0.7mm with contacts and 0.6mm without, i.e., 0.05mm for the contact. See:
beeforpork|4 months ago
https://www.usb.org/sites/default/files/USB%20Type-C%20Spec%...
Pages 42 and 44.