Hello, i just recently purchased a retail version of Fallout 3 GOTY and updated it to 1.7.
But when ever im around a semi-large amount of npcs my fps drops to 30-40 even on low settings. When i first got it and it auto detected it put my settings on low, which is weird because when it did that for skyrim it put it on high.
Here are my System Specs:

Operating System
Name Microsoft Windows 7 Home Premium Edition (64-bit)
Service Pack Service Pack 1
Build Number 7601
DirectX Version 11

System Information
Manufacturer HP-Pavilion
Total Number of Logical CPUs 4
Total Physical Memory 8.00 GB
Total Number of Optical Drives 3
Total Number of Hard Drives 1
Total Number of Video Cards 1
Total Number of Memory Modules 4
Total Number of DIMM slots 4


Motherboard
System Board
Chipset Intel G45/G43/P45/P43
Southbridge Intel ICH10
Base Board
Manufacturer PEGATRON CORPORATION
Product Eureka3
BIOS
Vendor American Megatrends Inc.
Release Date 01/28/2010
BIOS Version String 5.17
ROM Size 1.00 MB
Intel® Core™2 Quad CPU Q8300 @ 2.50GHz
Name Intel® Core™2 Quad CPU Q8300 @ 2.50GHz
Cores 4
Threads 4
Current Speed 2.49 GHz
Multiplier x 7.5 (6.0 - 7.5)
FSB Speed 1.33 GHz
Technology 45 nm
Features MMX, PSE36, EM64T, SSE, SSE2, SSE3, SSSE3, SSE4.1, XD, VMX
L1 Instruction Cache 4 x 32.00 kB
L1 Data Cache 4 x 32.00 kB
L2 Cache 2 x 2.00 MB

Memory
Total Physical Memory 8.00 GB
2048 MB DDR3-SDRAM (1333 MHz)
2048 MB DDR3-SDRAM (1333 MHz)
2048 MB DDR3-SDRAM (1333 MHz)
2048 MB DDR3-SDRAM (1333 MHz)


Local Disk
ST3750528AS ATA Device
Vendor Seagate
Model Number ST3750528AS
Serial Number 6VP1GCD2
Firmware Revision HP22
Size 698.6 GB
Rotation Rate 7200 RPM
Supported Standards ATA8-ACS, ATA/ATAPI-7, ATA/ATAPI-6, ATA/ATAPI-5
Specification Version ATA8-ACS rev 4

Display
HP 2009 (HP 2009 Series Wide LCD Monitor)
Mode 1600 x 900 (32-bit) (60 Hz)
Manufacturer Hewlett Packard
Serial Number 3CQ93106FH
Manufacture Date Week 31, Year 2009
Signal Type Digital


Video Card
AMD Radeon HD 6870
Video Card Chip Type ATI display adapter (0x6738)
Video Card Memory 1.00 GB
Driver c:\windows\system32\drivers\atikmpag.sys
Driver Version 8.930.0.0, 12-5-2011


Sorry about the wall of text if it is to much

Thanks, (This also happens to fallout new vegas but i dont play that anymore)

The game can not exactly handle many NPCs all at once, one the the cons of the engine being used.

i mean like in the room in the citadel where liberty prime is stored, i mantain a constand 30-40 fps in there
ive seen people with worse specs but run smoother then me

please help im getting really desperate D:

Look here: http://www.gamesas.com/topic/1348070-windows7-quad-core-fixes/