Tekken 6 Screenshots look almost exactly the same to me, of course there is a little difference with the background and maybe with AA (but you cannot tell from that one cause the ankle is at a different angle, might be that interfering...)
To SCIV vs SFIV comparisons, after more than 100 hours poured into SCIV, testing it on 360, playing a little on PS3-s, and closing to 600 hours of SFIV, played mainly on 360, and trying it with PS3/PC both:
1. SICV is higher resolution on 360, and also it lacks slowdown. There is almost zero slowdowns in PS3 version, but sometimes there might occur a little: that is not present on 360.
2. SFIV: I did not notice the AA difference much - I did notice the resolution drop in animations in winning/closeup scenes at PS3 -, and they both play at the same speed. There has been some great flame wars in SRK (for a while, I sadly took part in it, sorry -.-"), but the main consesus were that people were using different type of controllers (mixing wired, wireless, ps3/360),and different displays (ranging from upscaled, native, crt, lcd, etc..), thus almost everyone who switches from one type of setup to another with a different console/display will be off for a few matches, cause there is a difference -but it is not with the game's speed. It is just the latency of the setup which differs.