T'm too lazy type at this hour but something will assist you in taking the right decision, I'm quoting a post. All credits goes to the author
kirilmatthew said:
Here's the thing: laptop GPUs vary a lot between OEMs. One OEM can use GDDR5 while another can use DDR3. That's the main difference. Technically they could both be GDDR5 or both could be DDR3 or whatever. As for you, just remember that GDDR5 is wayyyyyy better then DDR3. If you can figure out what type of memory your GPUs have, then that would make the decision for you. If they are equal, go for the 8670M. If not, pick the GPU that has GDDR5. This may be tough info to find out, but if you search the laptop model you may be able to find out, you might not though. I hope you find out your answer and I hope this helps!(Source)
Besides that, this nifty little comparison chart is sufficient to gauge performance
8670m Vs 7670m
Edit: Now this is sad. I tried linking the exact page and there is no way to do so. You'll have to manually
restrict the two cards above in the options given. Just do Ctr+F and type 8670m and 7670m to select them one by one. Then vary the options given above and then click
restrict. You'll then be left with just those two cards
