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They're mostly the same as GeForce 600M series cards, except that clock speeds may or may not be higher. For example, is "up to 900 MHz" really higher than "up to 800 MHz"? Maybe. It depends on how the laptop vendor feels like clocking it.
There are some new cards there that have two Kepler SMXes, but only one memory channel, and DDR3 at that. If two channels of DDR3 was throttling performance way back, then what happens if you only have one channel of DDR3 memory? That's not going to end well if you had ideas about playing games on it.
The basic rules for the GeForce 700M series cards are the same as for the 600M series cards: if it doesn't have at least a 128-bit GDDR5 memory bus, you don't want it. The new single memory channel cards in particular will typically get crushed by AMD integrated graphics, and may exist only as a way for Nvidia to get rid of defective dies other than by throwing them in the garbage.