Help me choose

Make and model computer?

Other then "low energy" model card we don't recommend videocards to people using standard 300w power supplies.

HP Media Center PC m7265c.

Yea short of the real low energy cards like a a 6200le or 7300le , there aren't any high end cards I would run on the machines stock 300w. They will be fine if you just need a replacement gpu for basic use.

That being said even wit a power supply upgrade and a great gpu , this machine still is only using a pentium D so real newer or high end games will have problems.