If you build you own desktop you could easily get double the performance over any i7 laptop for the same price.
Some workstation cards just dont like to play games but do 3d rendering second to none. Gaming cards are capable of doing rendering but they are very slow compared to their workstation counterparts but will handle gaming with ease.http://www.notebookcheck.net/NVIDIA-Quadro-FX-880M.24735.0.html
Here is a site that has a lot of information and benchmarks of all kinds of laptop graphics cards. Some of the workstation versions, like the Quadro FX 880M have actual FPS results of people posting how good of FPS they got with that card. Its not a perfect site, not all the cards have FPS results for every game but it dose have "approximations" for many of the cards, I don't know realistically how accurate these approximations are. Hope this helps you out.