Dell Optiplex 780 upgrade

I have a Dell Optiplex 780 - small form factor machine - that I wish to do some gaming on:

http://www.dell.com/us/business/p/optiplex-780/pd

I have been searching for graphics cards for this machine, and found a few - this one included:

http://www.newegg.ca/Product/Product.aspx?Item=N82E1681...

It obviously may require a new power supply so I found this:

http://www.newegg.ca/Product/Product.aspx?Item=N82E1681...

...but I am not sure if that will fit. It looks too long to me, but I cannot be sure.

Dell's website has some options to upgrade this machine, but I am not sure the capabilities of them:

http://accessories.us.dell.com/sna/category.aspx?c=us&c...

The recommendation for power supplies is limited to 305 watt it seems:

http://accessories.us.dell.com/sna/category.aspx?c=us&c...

So my question: What should I do here? Does anyone know if the power supply will fit? What about the video card? Is it a good one?

I hope to play some Mechwarrior Online and Battlefield 3 with this until I can save enough for a real machine.

Any help or suggestions are greatly appreciated!