They are socket compatible: http://ark.intel.com/compare/75128,75117
Also, the i7-4800MQ supports VT-d where the i7-4700MQ does not.
However, you need to ask Lenovo if their BIOS supports the i7-4800MQ. Otherwise, you may find that it works, or only works partially, or does not work, or has damaged your motherboard.
thanks for the answer. So it seems that the risk does't worth the try. I've tried asking Lenovo support couple of times and they seem hesitant about the topic. Regardless, thanks again.
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Al Hill is right about this, the processor can similar and as well compatible with the socket but the BIOS in your laptop may not recognize the new processor and the laptop may never boot. You need to double check that your BIOS will support it. Some BIOS are very sensitive.