With the possible exception of very small twinkle spoons like Coho Killers, I think the longer leaders are more productive for spoons and for lures with their own action in general. The limiting factor is not having a leader so long that it interferes with effective netting, landing or releasing of the salmon. That may vary dependent on such factors as your specific boat design, the fishing regs at the time you are fishing (will you be releasing all or most without netting), net handle and rod length and if you fish alone or with a partner.