If VGA is important to you the ASUS has it but no Display port. Both the EVGA and ASUS cards will be great choices but I would be concerned about the EVGA superclocked because the 200 Mhz above ASUS may result in the requirement of a 6-pin. In the other versions it's purely optional.
Both...
The build you have only has a 300 Watt PSU which means the 750 and 750 ti are going to be your only options. The Superclocked versions may require a 6-pin connector for power so, based on these facts I will recommend this product:
http://pcpartpicker.com/part/asus-video-card-gtx750tioc2gd5...
Are you aware of what Computer pre-built you have?
This will help us give you advice and identify your PSU.
The GTX 660 and 750 ti are going to be your best bets as both require less than 500 watts to work. Both will be comfy at 450watts and the 750 ti will want much less. If you plan to go...
Something to keep in mind is games are growing more demanding on VRAM and 1 GB cards such as the HD7850 or GTX 750 or some 260Xs are going to soon become obsolete without that added buffer. Plus it also makes modding skyrim more fun :)
What is your PSU? Most should support a GTX 660, some may...
The 750 ti and 750 would be a much better choice and are around same price as a 650 ti. Here is going to be a good list for you: Some older generation AMD cards dominate in value such as the HD7870 Ghz edition for $130...
you should definitely go for 8 GB Ram unless you aren't doing gaming or something that needs ram
(like hundreds of tabs open in firefox)
If you choose to keep your current to 4 GB, I would say option 1, 1x4 GB.