Like lots of PCSX2 users, we all obsessed by the superior graphics capability that PCSX2 could provide, but when we increase the D3D internal resolution for games, glitches occurs, the most notable problem is numerous obvious vertical lines run across the screen, like the following post.
people guessing that we can solve the problem by trial and error since changing the internal resolution would somehow affect the position and number of vertical lines.
I've managed to get a perfect resolution yet high enough for FF12, the game that I wanted to finish on nice graphics with PCSX2.
Here is it
1536 X 1344
Actually, try to pay attention to the left upper corner, it shows the original resolution of the game (like FFX-2, it uses 512 X 416), and try to multiply this value when modifying.
hope it helps