Here's the benchmark for GT 740m http://www.notebookcheck.net/NVIDIA-GeForce-GT-740M.89900.0.html
You can play BF3 at medium settings with playable frame rates. The HP Envy 15 at 4.81 lbs is on the chubby side of the ultrabook family. Acer Aspire and Macbook Airs are all under 3 lbs but they only offer integrated graphics.
If you want an ultrabook that can do some medium gaming then HP Envy 15 isn't a bad choice.