I guess the only real benefit of presoaking would be to control temperature, which is what I do it for. Plus it looks really cool when you pour out that green-blueish stuff. On a side note, Fomapan never curls with me, it dries very flat when I hang it to dry.
Is there any other developer than Pyro with hardening properties? I really love Fomapan, but I've almost given up on it because of the scratches.