Graphics card suggestion

Have a bump, probably someone is typing a huge ass comment so don't worry :P

I upgraded from a 9800gt that died to a 750ti and have had no issues.

Also, on the links you posted the 2nd link shows no indication of it being the OC version anywhere on the box as opposed to the ebay link.

I personally think you would be better off waiting a few months for the prices to drop in the 4th quarter and maybe upgrade to 8gb ram with your gpu if you can find decent prices.

I am a firm believer in upgrading your heart first, so I would personally upgrade the CPU first to avoid any type of bottleneck issues you may see down the road with an upgraded GPU.

put this entire computer somewhere else and buy a brand new one with chosen pieces

you can't upgrade anything there, everything's to change

This rig is way too old to spend money on brand new parts. Get some second-hand GPU and start saving up for a new computer instead. A 750 Ti is overpowered for this one and will be limited by the CPU, but not strong enough to actually last long for a potential new computer in the future
If you can get a GTX 500 series for a decent price, or a Radeon HD 6000/7000, then go for that..

With your setup I recommend a less expensive card, as you don't have a whole lot of RAM and a badass gpu won't give you as much of a performance boost as you would like unless you upgrade your memory. Try the radeon sapphire r7, it's an upgrade from your current gpu and it's only about 50 bucks. I use one myself and I can play everything I own at maximum settings. It is pci-e x16 2.0, 2gb vram, and I think 750 MHz clock speed if I remember correctly. For the price tag it's a nice little powerhouse of a gpu.

As for the pictures, there are different models of 750Ti. The second Gigabyte one you linked (larger card, two fans, etc.) is one that is marketed towards enthusiasts. Normally, a 750Ti does not require an extra PCI-E power connection. It takes its power right from the slot. But that one marketed for enthusiasts has an extra 6-pin PCI-E power connection that gives it more headroom for overclocking. The dual fans are there for the extra heat given off by overclocking as well. The first 750Ti you linked seems about right. It's normally a small card and has no need for an elaborate cooling solution because you really can't get the temps up too high on them without an extra PCI-E power connection.

EDIT: Just noticed and it is possible that the picture on that Ebay item might be wrong... That looks like a plain 750 much less a Ti. The 750Ti OC does look like it is a bigger card with dual fans. Sorta the reason I stay away from ebay for things like that. The only way you can be sure is to compare model numbers.

A 750Ti is OK. It's probably one of the best budget GPUs available. But as others have suggested, it's not exactly future proofing your current computer. And if you choose to upgrade your computer, it's a good GPU, but you will probably find that it will be your bottleneck (unless you don't mind running things at only moderate quality settings).