Graphics Card Compatibility

Solution
You have a very powerful CPU (i5-4670) that can handle the best GPUs for 1080p-resolution gaming (GTX 1060 and RX 480) without bottlenecking their performance. Of course, the upgrade would entirely depend on your budget (as well as considering upgrading the PSU to a good-quality ~500W to power such GPUs).

For me, going from a GT 640 to a GT 710 is a minimal increase in graphics power (again, may be due to your limited budget), but an increase nonetheless.

I don't know the specs of your 300W PSU. But you can get by (depending on your actual PSU's +12V and quality), a GTX 1050 or GTX 1050 Ti.
Any graphics card with a PCIe interface should fit/work/be compatible (not PCI, not AGP, but PCIe).

How powerful the GPU is would entirely depend on your CPU's capability in handling the GPU's performance without bottlenecking it.

There is also the factor of what PSU wattage/amperage you have if it can power your GPU as well having the appropriate number of PCIe power connectors if required.

Another factor is the clearance length of your case if the GPU would fit inside.

Last factor to consider is the monitor resolution/refresh rate you are using.
 


Thank you for your quick response.

My systems has:
A full size desktop case
Operating system: Windows 10 Home 64-bit
CPU: Intel Core i5 4670
Motherboard: ASRock B95M-DGS
RAM: DDR3 1 x 8192 MBytes
Graphic: NVIDIA GeForce GT 640
PSU: 300 watt
Monitor: 24" AOC with 1080p, 1920 x 1080 (native) resolution.

Would a Gigabyte GT 710 2GB GeForce Silent Video PCIe 2.0 nVIDIA Graphics card be a suitable replacement/upgrade?
 
You have a very powerful CPU (i5-4670) that can handle the best GPUs for 1080p-resolution gaming (GTX 1060 and RX 480) without bottlenecking their performance. Of course, the upgrade would entirely depend on your budget (as well as considering upgrading the PSU to a good-quality ~500W to power such GPUs).

For me, going from a GT 640 to a GT 710 is a minimal increase in graphics power (again, may be due to your limited budget), but an increase nonetheless.

I don't know the specs of your 300W PSU. But you can get by (depending on your actual PSU's +12V and quality), a GTX 1050 or GTX 1050 Ti.
 
Solution


Thanks for your reply. My budget is limited to about A$100, so I might have to stick with the GT 710 (about A$70) or Gigabyte nVidia GeForce GT 730 2GB DDR3 Graphics Card (A$98).