I'm also very curious about the achievement difficulty. I maxed Tekken 6 with ease, and have complete SF4, SSF4, MKVsDC, and MK, but I still stand by the fact I am awful at fighting games.
I only maxed the above through pure patience, frustration and it took me a couple of years lol. I have maxed Soul Calibur 4 but hated it, I have Soul Calibur 5 on my shelf, but not sure when I will get round to it. I have to say though I do love Tekken series a lot, and if the achievements are reasonable I might have to go buy it this weekend.