INI:
Ugridstoload=7
uinterior cell buffer= 12
uexterior . . . = 144
Absolutey should not mess with those. uGridsToLoad set to anything above 5 will lead to what's called the bouncing landscape bug. Makes getting around quite difficult when it hits. The other cell buffer settings have been largely proven ineffective by people who have seen the code and know their stuff.
ipreloadsizelimit = 262144000
Jury's still out on this one.
MEssing with any of the water settings is known to cause issues, including the reflections stuff which is more recently being singled out as a major cause of FPS issues.
most multi thread and background loading enabled
Also entirely ineffective. The OBSE team has examined these in detail and concluded that none of them are even used by the game.
The cold reality of it is, Oblivion is just poorly optimized for PC. Which is a shame.