Oblivion:Ini Settings – en.uesp.net
uExterior/Interior Cell Buffer
uGridsToLoad controls the distance at which LOD objects and textures are scaled to their full quality. Changing uGridsToLoad is not recommended, as it may significantly reduce performance, and has been found to cause issues with the LOD aspect of Oblivion.
The Cell Buffer related settings control the maximum amount of "cells" that can be stored in RAM/Video RAM at once. Increasing this will allow Oblivion to cache more textures/objects into RAM, so increasing these values will yield a performance increase for computers with enough RAM (1.5GB and up) Note: The extra 'buffers' are primarily loaded into your video RAM, which may cause problems. Keep this in mind when adjusting these values and always make sure you have 50-100MB of spare video RAM.
iPreloadSizeLimit sets the maximum amount of data that can be loaded into memory whenever the game loads an area (when entering and exiting an area, i.e entering/exiting a house, fast traveling, basically whenever a loading screen appears).