Hi
The only success I have ever had catching kob on artificials was in Henties with Havoc lures, I know some EC guys also have good success with Havocs. We used a very slow retrieve. If I'm not mistaken the havoc lures are locally made somewhere in the EC.
The havoc lures also have weighted hooks (both hooks), so I assume pretty much the same as the rapala you described.
I have also read quite a few posts (haven't tried myself yet) about cathing kob with s-bend spoons, slowly retrieved so that the spoon bumps againts the bottom. This seems to be the way to go as everyone always suggests this.
I would also try a bucktail jig, bouncing this off the bottom, this also seems to work like a charm.
So, based on everything I have learnt from the guys in the know I would say a slow retrieve close to the bottom is best for kob.