Max RAM is depend on the MB's northbridge (for intel) that has the memory controller, and is not depend on the CPU. So if the lenovo says up to 8GB ( I check it too), that means it can use up to 8GB RAM. If you use the 16GB RAM most of time the PC will not boot.
Your board is based on the intel H61 northbridge which supports 16gb (2x8gb). However, since Lenovo says it will only support 8gb, I would check with their customer service folks before buying 16gb. I can see no reason why 16gb would not work, but I'm sure the Lenovo motherboard is "proprietary" and it may be artificially limited by Lenovo. Check their forums also.