The 518, specifically 2nd version of the mouse had max IPS issues with drivers installed. This was because the drivers would scale and interpolate down from the native 1800 CPI step instead of the 800 causing a bottleneck in performance. I forgot if the original 518 had this issue, but the native steps were different than the re-release. 400-1600 instead of 800-1800. "Different sensors" if we want to get specific.
The G400 also shared this issue, although it was fixed rather quickly and now properly scale when at or under 800 CPI.
To answer your question: You would be better off with the Logitech drivers instead of artificially decreasing polling rate.