http://ark.intel.com/ProductCollection.aspx?familyId=43...
They all can hyper-thread but for gaming this isn't really utilized vs. using more cores.(Even for that, games don't require having a quad core yet but it helps)
Judging by that list, for the i7 Q means no integrated graphics and is a quad core cpu. And M just means Mobile. The U in the name means low wattage (15 watts). The L I don't know exactly but it does have lower watts (25watt).
i7 920 is the Desktop processor .
All the i7 6xx series have 4mb cache and come with intergrated graphics , 2 cores / 4 Threads
All i7 7xx series have 6mb cache , 4 cores/ 8 Threads
All i7 8xx series have 8mb cache , 4 cores/ 8 Threads
The i5 's have 3mb cache , 2 cores / 4 Threads
i can see why the i5's can be just as good as the i7 6xx series. Specs are so close, I do not see why Intel has to confuse everyone with their weird naming schemes. A lot of these mobile processors seem to overlap over each other.
Also more watts means more heat, but if i were in your shoes I would stay away from the low wattage ones without researching their performance. And I use a notebook cooler myself and will never seriously game without one. (Just because I can feel the heat through the keyboard and makes my hands sweaty)
If you can spec out a few laptops at ibuypower or anywhere else and post them here. I'll check out the specs online and see if i can get any good reviews online.
And another thing, I'd buy the best mobile video card I can because usually they are very hard to upgrade. A lot of laptops can have their cpus upgraded as long as the socket and motherboard can support it. For graphics, manufactures like to make their own custom crap video cards to fit into their laptop shells.(so they can't fit into any other model/brand laptop)
Also, For gaming, just get the fastest processor (either i5 or i7) with the most speed as you can get. 2.0ghz and up minimum to play games. That and the fastest graphics you can fit into that laptop. Graphics above all else for a laptop + cpu speed for gaming.