Need help finding graphics card upgrade (Alienware X51)

Hi Guys,

I have an Alienware X51 with an NVIDIA GeForce GT 545.
I'm able to play GTA 5 without any problems. However my PC gave up when I tried to play Assassin's Creed Unity  
Thats when I figured I need an upgrade.
Can you guys please suggest a suitable graphics card (that would fit in my cabinet) for the following configuration:

Motherboard

Manufacturer Alienware
Model 08PG26 (CPU 1)
Version A00
Chipset Vendor Intel
Chipset Model Sandy Bridge
Chipset Revision 09
Southbridge Vendor Intel
Southbridge Model H61
Southbridge Revision B3
System Temperature 28 °C
BIOS
Brand Alienware
Version A14
Date 11/4/2013
Voltage
+3.3V 3.280 V
CPU CORE 1.352 V
VIN2 2.208 V
VIN3 1.200 V
+5V 3.237 V
+12V 14.872 V
VIN6 3.280 V
VSB3V 3.280 V
CMOS BATTERY 3.296 V
PCI Data
Slot PCI-E
Slot Type PCI-E
Slot Usage In Use
Data lanes x16
Slot Designation PCIE
Characteristics 3.3V, Shared, PME
Slot Number 0


Graphics

NVIDIA GeForce GT 545
Manufacturer NVIDIA
Model GeForce GT 545
GPU GF116
Device ID 10DE-1241
Revision A2
Subvendor NVIDIA (10DE)
Series GeForce GTX 500
Current Performance Level Level 3
Current GPU Clock 870 MHz
Current Memory Clock 2000 MHz
Current Shader Clock 2000 MHz
Voltage 1.025 V
Die Size 238 mm²
Transistors 1 M
Release Date May 2011
DirectX Support 11.0
Bus Interface PCI Express x16
Temperature 46 °C
Driver version 9.18.13.1106
BIOS Version 70.26.32.00.01
ROPs 16
Shaders 144 unified
Memory Type DDR3
Physical Memory 1023 MB
Virtual Memory 736 MB
Bus Width 192 (192 bit)
Filtering Modes 16x Anisotropic
Noise Level Moderate
Max Power Draw 70 W
Count of performance levels : 3
Level 1 - "Default"
GPU Clock 50 MHz
Memory Clock 101 MHz
Shader Clock 135 MHz
Level 2 - "2D Desktop"
GPU Clock 405 MHz
Memory Clock 810 MHz
Shader Clock 324 MHz
Level 3 - "3D Applications"
GPU Clock 870 MHz
Memory Clock 1741 MHz
Shader Clock 2000 MHz

PSU

DPN : J211H

100-240V ~3.5A 50-60 Hz

I was suggested the GTX 1060 FE blower type version by a friend. However that is a bit expensive for me.

Can you guys please let me know some other options as well.

Appreciate your help