John Ashley- Cooper who landed a few salmon in his time states that it should only take 30 secs/pound so you should land a 10lb fish in 5 minutes. Bear in mind that JAC would have usually used a gaff, and would have killed most if not all he landed.
In more enlightened times. 1lb/minute when beaching or netting is probably more reasonable. On the Spey where the current can play a big part a large salmon can be quite an handfull.
I had a 20lb fish last Saturday, alright I just love saying that, and I had it beached photod and back in the water in under 20 minutes.