Definitely go for a hd7750. I do not know if you need a low profile card or not. All you have to do is make sure you get a model that does not need a pci-e power connector. I have the HIS icooler hd 7750 and its performs fantastic for a 55watt gpu at 1080p and it pulls all its power from the pci-e slot.
His low profile card takes 2 slots so if you need a single slot card sapphire makes one. Also make sure whatever you buy has GDDR5 mem not ddr3.