Do not use these chains for derailleur bicycles; they are designed for use with internally-geared hubs with a single 1/2 x 3/32 sprocket. They're very strong (particularly the 7E8 and 7R8), but they're not flexible like a derailleur chain. For 6-, 7-, and 8-speed derailleur bikes, use Connex 8-speed chains.
The best choice? 7R8, and it's electric cousin 7E8. Both come with bushings and are reinforced for heavy service.