I'm back, after a couple of days away with my travel kit.
Test set up as described in this thread here. This test compares a Personna Med Prep blade and an Iridium Super. I'm using two EJ razors, one black handle and one white, and I don't know which blade is in which.
White = right side of face
Black = left side of face
Brush = Vie-Long Horse
Soap = Body Shop Maca Root cream
AS = DR Harris Windsor
Pass 1, WTG: Both still good, but I think they're both just starting to lose their sharpness a bit now. White felt a little better, and close inspection after this pass showed that White had shaved me closer and there was definitely a little more stubble on the Black (left) side.
Pass 2, XTG: They felt about equally good going XTG, but White gave me a small weeper on my upper lip. Closeness after two passes was about equal.
Pass 3, ATG: I thought Black was losing its sharpness on this pass. It wasn't really noticeable over most of my face, but ATG on my upper lip was getting a bit tuggy - and that's where I usually first notice a blade losing its edge.
Closeness: Finally closeness was pretty good. Both sides would have needed a bit of buffing under the chin to get BBS, but I'm not after that - but easily a DFS.
Comfort: After drying, the left (Black) side of my face felt like it had been shaved the hardest. Not uncomfortable, but not as comfortable as the right (White) side.
AS: The new DR Harris Windsor, which has a fantastic fragrance, gave me a nice tingly glow, but a bit more towards stingy on the left (Black) side of my face. I think it's fairly clear that Black gave me a slightly rougher time of it this shave. But that's after the equivalent of 4 full face shaves each, which is already a decent life for a blade.