Will this card fit my system? Optiplex 755

I understand that you want the stronger, the better option is this correct? If yes lets look at your options.

First thing to know, PCIEx16 version 3 is back compatible to V2 and V1, your bandwidth will be limited.

However newer cards run cooler. If your CPU will bottleneck GPU too much, you might see some artifacts when playing games, just to know.

There are a few obstacles you have to remember.
First. GPU must be low profile or must have low profile bracket, something like this

Strictly low profile card



Low Profile Brackets - regular size bracket removed and low profile is installed, user usually sacrifices VGA port
This is how low profile brackets looks like (user must check if manufacturer included those brackets)



Second. GPU must be single bracket



Mini Tower, but problem is the same


Third, it better be shorter than 7.5 inches - distance from back panel to CPU shroud, it can be longer only if it is very skinny, with width not to exceed size of the single bracket, more or less, then it may squeeze nxt to the shroud.
Picture below illustrates Optiplex Mini Tower which has the same size CPU shroud, except may be Desktop or Small Form Factor CPU shrouds are not that high, but width and depth are the same.



Forth. GPU height is very limited despite low profile, because your hard drive is located directly on top of your GPU.

Example of the card which would not allow for hard drive holder to fit


Actually user reported that he had to trim hard drive holder to fit this card

Good card.



Fifth. Optiplex 745 and Optiplex 755 motherboard have a few tall capacitors close to PCIE slot, card with large fan shroud can not sit properly in the slot.

Your motherboard issue



Bad card, cannot fit



Good card



Those are all restrictions to deal with.

These are the options

[strike]EVGA GeForce GT 740 02G-P4-3740-KR 2GB 128-Bit GDDR5 - it is the same size as your choice.[/strike]
Someone just reported an issue with almost the same card http://www.tomshardware.com/answers/id-2773466/faulty-card-drivers.html so skip this choice

PNY GT 700 GeForce GT 740 VCGGT7401D3LXPB 1GB 128-Bit DDR3

Maybe you can find others similar, but it is not an easy task as you have to avoid 5 obstacles.
Good thing to know, your PSU will support those cards with ease.

I think you are set.