Everyone seems to have missed the part where he asked for Low Profile.
Unfortunately none of the newer GPUs are available in low profile, inf act the only "good" low profile GPU is this one:
http://www.newegg.com/Product/Product.aspx?Item=9SIA24G2NU2973&cm_re=750ti_lp-_-14-125-680-_-Product
Its is low power as well and won't need external power from your PSU.
Because of the size of that case there are no PSU upgrades you could do on it. Its a non standard size, proprietary to dell low profile cases.