SeduceMePlz: I recall reading an article about mobile GPUs catching up with desktops these days, but I don't have a link handy or remember the site.
Shadowstalker16: They are getting more powerful, to the rate of being more powerful than many high ends GPUs of the previous generations, b
ut the sheer higher amount of power, space and cooling available to newer GPUs still makes them quite weak compared to them. Temperature is a big issue here, since higher clocks = higher temps and laptops aren't very good at cooling the GPUs and don't have good airflow or size to disperse the heat. Power will also be an issue since getting so much juice from a battery is so difficult.
This is not really true anymore, as some Laptops can run a 980, which is nearly as fast as the desktop 980 and the 980m is 10%-15% slower than a normal 970. The 970m beats the normal 960. So you can play without a problem wih a laptop with the right cooling system. The monster gaming laptops like the GT series ave a very good cooling system, although it gets loud when on full power.
Just take a look here to compare desktop and laptop GPUs:
http://www.notebookcheck.net/Mobile-Graphics-Cards-Benchmark-List.844.0.html Now coming to buying a laptop. You can easily upgrade HD and often Ram in MSI laptops and even video cards in the GT series. My GS70 for example has 2 msaa slots for SSDs which can be put in within 5 mins,
For power gaming i would not recommend a slim model, as they tend to get quite hot and then throttle, so GT series is the best for a power gamer who lets his laptop at home. GE series for me is best jack of all trades with 970m and great ability to expand. I would not buy the lower series as they dont cost much less.
Gaming laptops are not built to play high usage games without power plugged in, else you have way lower performance and well, after an hour or so no power at all ;)
HereForTheBeer: Capabilities: play muh games, office work, portable for on-the-spot access, portable for ease of the travel schedule, will last several years while still being able to play said games, 17" screen, full keyboard (backlit would be good). 4+ USB ports. HDMI out. Optical drive would be nice but not required. Maybe some other details that com down to personal preference.
My choice would be a MSI GE72 with 970m and 8GB Ram and no SSD, then buy another 8GB Ram and a m2 SSD of your choice and plug them in easily. This one has 3kg, so still quite mobile and as it is noot too wide can fit in bags easier than the high end gaming laptops. I use an Eastpak Goof with my GS70 for some years. For a gaming laptop you will not find many cheaper alternatives with FHD ;)