"Correct" way to attach cable to this specific kind of banana plug
This type of terminal is intended to be soldered in the way you describe.

Check carefully the interface between the spring cage, and the pin. I bought some cheap 4mm plugs which failed to make a secure contact between the inside of the cage and the outside of the pin. The I/D of the cage was too large, and rotated easily on the pin, even when the spring cage was compressed in the right size hole. Even if it rotates easily initially, it should tighten to the pin when inserted into a socket. I would be nervous about passing 8A through the connector if the pin to cage connection was poor. 

I ended up soldering (very quickly and carefully, to avoid solder wicking into the cage (after trashing one that way)) the cage to the pin on the leading end, for my peace of mind.