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.
I want to upgrade my precision 5520 so I have to make sure if my laptop can support 2666Mhz ddr4 ram (corsair vengeance 16GB x2 2666MHz). If it can so will it works with full speed or just 2400Mhz? I’m using two 16gb 2400Mhz rams so is there any difference in speed if I replace them with 2666Mhz ones? Hope someone can help me, thanks    Looking for earliest reply   
Precision 5520 Ram Maximum speed support