Precision 5520 Ram Maximum speed support

Dell specs call for DDR4 2400 and if you have a 6th gen CPU 2133. If you install 2666 it will probably run at 2400, besides the difference between 2400 and 2666 is slight and will make a minimal difference in performance if at all. Corsair may work but Crucial RAM is the most compatible and most recommended RAM for Dell systems.

If you are running 32GB of 2400 now, there is really no reason to spend the money to go to 2666.

Dear Jocean thanks for the reply

I am running on i7 7th generation and i want to upgrade my laptop with crucial ram with 2666. (16x2Gb=32Gb)

Is it safe to go with 2666 frequency, first time i am going to upgrade my system.

I don't want to compromise with performance

So will you suggest me to buy this ram 

Crucial RAM 32GB Kit (2x16GB) DDR4 2666 MHz CL19 Laptop Memory CT2K16G4SFRA266.

Thanks in advance 

That RAM should work, but it will not run at 2666. It will downclock (run slower) at 2400. Dell specs and Intel specs for your processor both state maximum speed as 2400.

Crucial shows a list of compatible RAM for your system. Most are 2400. Some are 2666, but they will run only at 2400. 

Whenever touching components or working inside a computer, wear a grounded wrist strap, also called anti-static wrist strap, ESD wrist strap, or ground bracelet. I know many people do such work without this, but it's a cheap and sensible precaution. Rest the laptop on an anti-static mat or at least a reasonable alternative such as corrugated cardboard.