I'm still getting used to the Slim Adjustable I'm now using. I did start off with feathers in it, as I'd found in the DE89 they gave me the easiest shave, but the feathers gave me a poor shave, so far.
Until about 10 minutes ago I've struggled with the Slim to get a good shave. Yesterday I wasn't completely smooth but I had to stop as I could feel irritation coming. However I had probably the best shave I've ever had tonight, and that was with a Gillette Super Thin Platinum, and the adjustable dial set to 4.
I will go back to feathers, of course, since I've got 50 of them sitting in the cupboard... but I'm going to be investigating lots of blades to see what works best.
Something that I find makes it difficult to really judge a blade is controlling all of the other variables. How do we know, for example, that our stubble is at the most pliant it can be, or how do we really tell we got a great lather from the shaving soap/cream rather than just a very good one.