RAM upgrade

Hi there I'm new to the forum, I'm here today for a quick advice.

As per the title, I'm planning on upgrading my RAM memory to 128GB on my mobile Precision 7750. Now, I currently have 64GB (non-ECC) @3200 MHz, but just a single stick of 32GB @3200MHz, non-ECC is crazy expensive!

However, I found a good deal for 64GB (2 × 32GB), non-ECC @2666MHz, and I was planning on buying two of them, then upgrade the RAM on my machine.

The question is, is there any substantial difference in having 128GB @3200MHz vs 128GB @2666MHz? What I normally do is data analysis on genomic data, and most tasks are heavily reliant on RAM; in fact most often information are fully loaded on the RAM, and only once the execution is completed files are generated on storage memory.

Let me know what I should do, also considering the not negligible difference in price. Going for the option @2666MHz would result in a saving of ~700$!

Thanks in advance.

FYI these are the specs of my machine