Which one is better for gaming?

Solution
HD 7970M is better

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Since you added the 7970M, I'd suggest going with that instead. SLI although having more potential power, also has issues in certain games.

So a single GPU the 7970M is still very good for a mobile gaming card, will use less power, produce less heat and not have SLI related issues.
 


sorry mate, your talking through your hat. There's no comparing the 750 sli to an HD7970. The 7970 is far and away above. Even if you had an sli gtx765m (which are good) they would only barely beat the 7970.

You are correct on one thing though, SLI is more heat, and can have driver issues. Anyway, to OP always go for the most powerfull single solution GPU setup that you can afford.
 


mobile variants are always slightly different than their desktop counterparts, that's to do with power consumption mainly. So the mobile parts will always be clocked lower, and maybe even are built on old tech (case in point would be the 750sli's mentined above, which are actually rebranded 650's!!) The 7970m is a really good GPU, far and away above the others mentioned in a single GPU setup, and would beat all bar the 765m sli (and that's just a maybe). The GTX765m is also a rebranded older gen GTX670m. before giving answers do a little research.
Some people will go and purchase based on our recommendations, and we don't want to be wasting anyone's money, no, do we?