I don't see any problem. You can even use a dual slot card if you prefer. 100% of the card's thickness will extend 'downward' looking at your pic, if that is your concern. So there is no issue with using even a wider card. It would cover one of the PCie X1 slots, but no big deal if you don't need it. The card's length is so short, that it is no issue either.
In fact, if you want an even faster gfx card that will run on your stock PSU, look into the GTX 750 Ti. Fastest card available that needs no 6 pin cable.
I had this one in a previous machine:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
It can play Crysis 3 at mid settings at 1080p.