I was wondering if anyone has experimented with raising the UgridsToLoad value? I know in Oblivion it causes problems, but I'm not sure about Fallout 3 or New Vegas. I've been running my game with the value set to 7. I like the visual enhancement it gives and for me the performance hit is negligible. I tried running with the value at 9 but the performance hit was noticeable. I haven't seen any bugs or glitchyness yet I just wondered if anyone else had different results?

For info, my system specs are

WinXP SP(whatever the latest update is)
4 gigs of DDR2 (or however much the game uses)
AMD Athlon X2 2.6 MHz
ATI Radeon HD 5770 1 gig

Also - all the detail sliders are turned up all the way & whatnot
resolution - 1600x1200
Anti-Aliasing - 4x
Anitropic - 15

had mine up to 11 with no major performance problems, make sure you increase the exterior cell buffer too though.

this is from http://www.tweakguides.com/Fallout3_8.html, for FO3, it works well for NV too, theres a lot more you can do i would recommend checking it out

uGridsToLoad=5 - Increasing the uGridsToLoad value (always in odd steps of 5,7,9,11 etc.) will increase the number of grids around the character in which full texture and object data will be loaded up and visible as they wander around. This improves overall visual quality by increasing graphical detail on more distant game world elements. Indeed certain objects and structures which were otherwise not visible before will now be visible. The higher the value, the more you will see of the game world in return for a sharp drop in framerate, and noticeably longer loading times. There may even be more prominent stuttering as well, not to mention the possibility of visual glitches and the greater likelihood of crashes due to the extra memory usage. Unlike Oblivion, in my testing using a value of =11 I didn't see any visual glitches in Fallout 3 at all, however my performance fell by more than half, and I eventually experienced a crash to desktop. As you increase the uGridsToLoad value, you may want to also increase the uExterior Cell Buffer value to accommodate the greater cell data and prevent crashes and stuttering. Note: It appears that if you save a game with a higher value for this variable, you cannot then lower the value again as your saved game will no longer load properly. So on balance the default value of 5 for uGridstoLoad is a good compromise between visual detail, performance and loading pauses, though high-end machines can try higher values, but make sure your system can handle it in a range of areas before committing to it by saving your game (Fallout.ini).

fBlockLoadDistanceLow=50000

fTreeLoadDistance=40000

These two variables are actually quite important for overall Level of Detail. They correspond to the Object LOD Fade and Tree LOD Fade settings available in the Launcher options and are covered in the In-Game Settings section. In effect they determine the visible distance for buildings and trees respectively. In the Launcher they're restricted as to how high you can raise them, however here you can raise them to very high values (e.g. to =500000) and thus increase the number of buildings, objects and trees visible in the distance. Furthermore the performance impact seems minimal at best, and certainly is nowhere near as high as the uGridsToLoad variable which does something similar (FalloutPrefs.ini).

fSplitDistanceMult=1.5 - This variable is the same as the Land Quality Launcher option (See In-Game Settings section). However while the Launcher slider only goes up to a value of 1.5, by raising it further here (e.g. to a value of =10), you will get a more noticeable increase in the level of detail in distant landscapes, although FPS will similarly be reduced by a noticeable amount (FalloutPrefs.ini).