FWIW, I find the differences of the PPI Gillette Blades to be largely noticable.
I've used most of them and I've found there are ones which are very sharp (eg 7OC Yellow), sharp and smooth (Polsilver, Permasharp), smooth (Gillette Platinum) and the others which fit kind of somewhere between the ones named.
There are a couple which are fairly close to each other, I found Polsilver and Permasharp to be fairly close to each other, especially after a few shaves. Like SeanC, they are my favourite two blades as well.