OK gents, update. I just finished a shave with the Merkur (which I shall shortly post in SOTD) and I'm very pleased with the results. Thanks to all the opinions and suggestions received from your good selves, that was the best shaves I've had with this razor for a long while. I think the biggest factor was possibly a change in blade types, from Crystals (which I've now used up) to SuperMaxes, which I've been using in the Slim with great results. I suspect that the Crystals didn't agree with me. However, I'm sure that maintaining a light grip as so many of you mentioned, combined with looking at the photos I linked to previously showing optimal blade angle for the Merkur helped enormously also. In other words, doing what most of you seemed to agree was important - to stop myself from being too cocky and going back to basics. In future, every shave will be accompanied by me going through a mental checklist of "light grip, angle and moving the whole arm, not wrist".