It's strange but i have no performance decrease with 8x FSAA, maybe it's because i'm running Dolphin at 1600x1200 (19" CRT monitor) and my video card has 2GB of VRAM which is more than enough for this resolution ?
As for texture cache - RAM and safe will be slow even on most powerful PC.
As for texture cache - RAM and safe will be slow even on most powerful PC.