The fastest possible speed of hard drive I could hope to install?

Basically my Macbook Pro (Late 2011) has become increasingly slow over the years so I'm looking to upgrade my hard drive. I was initially looking at putting in a 'Samsung 960 PRO V-NAND NVMe PCIE M.2' and then buying an adaptor to replace my 2.5 SSHD such as the 'DELOCK 62786' but then after doing some research I'm not sure if that would work, or even if there would be any point whatsoever in doing so due to the link speed in my macbook (also can I do anything to change the link speed?)

Is there any way of utilising the ExpressCard/34 slot on the side of the mac to add some storage?

Failing being able to install a 'Samsung 960 PRO' could I install a 2.5 'Samsung 850 Pro SATA III' as I think I've read that the link speed of my Macbook Pro (late 2011) is only a SATA II. Is there any way I can check? SATA II I think only allows speeds of up to 3GB/s and SATA III is 6.

Apologies for my barrage of questions and ignorance, and thank you in advance.