I don't really consider the slant to be an "aggressive" razor and open combs can vary all over the map on aggressiveness. I really like the Gillette blacks and Feathers in my slant, but find that it tends to make most blades feel sharper. Open combs really vary on the particular razor.
True enough about open combs-they're all over the place ala' aggressiveness. Now the Slant-that's my daily razor...I don't think it's aggressive but it is efficient. Also, I've found that just about any blade will work in this razor. Right now I'm burning Derbies in the Slant and then will switch over to Astra SP for awhile as they give nice shaves.
In my R41 it's very much Bolzano, Feather or Astra SP. the only mild blade that's worked for me in that razor is a Racer which is very nice but in general the sharper the better. Just seems to make life easier.
I have some Gillettes to ry and from what I read these may be ok as well but blades like Shark SC are a big NO in that razor for me and yet I originally thought these were sharp and smooth in my EJ razor.
I have a 20's vintage Old Type and so far have found that it loves most of what I put in there. Personna Super labs, Ladas, and Astra SPs work great in it, but Laser Super Stainless do not. Now if those are sharper or less sharp blades, I don't know.
Gillette 7 OC black and yellows; Rapira stainless, Voskhods, Ladas, Personna Med Prep, Polsilver-that oughta hold ya for awhile. They all work well in the Progress, Fatip and the 39C.