I have recently acquired a heavyweight all stainless steel Ikon S3S with the bulldog handle. It is a beautifully made razor and gives a super close shave. The only problem is that is seems to suffer very badly from the first shave on a new blade phenomenon, even with corking. I have so far tried Feather Pt, Derby Extra, Gillette super thin yellow, and Dorco Pt and all seem the same. My way round it has been to do the first shave with the new blade on my Gillette Super Adjustable, which is probably the mildest of the user razors I have. I set at 3 rather my usual 4 or 5. I do have a WW2 Feather which is even milder but I regard that as a collector not a user. After one day's break in with the Gillette, the blade is then perfect for use in the Ikon. For me Derby Extra seems to suit it best.
Wilson
Wilson