Sensor

The M55 uses a PixArt PAW3327 optical sensor. While still pretty great, it is more of a mid rather than high tier tracking unit. It's very raw and responsive and provides snappy feedback, and while based on the PMW3320, it has some improved features, such as a higher perfect control speed and resolution. I've tested mice with this sensor a couple of times already, and it never seemed to fail.

As for its technical specifications, the nominal maximum tracking speed and acceleration values are 220 IPS and 50 G. The resolution can be set from 200–12,400 CPI in steps of 100 CPI. Anything above 6,200 CPI is interpolated given that is the maximum. Available polling rates are 1000, 500, 250, and 125 Hz, which are respective nominal response times of 1, 2, 4, or 8 ms. The lift-off distance is rather high at above 2 DVDs (2.4 mm) on a plain black cloth mouse pad.

Paint Test

There is no jitter on the reasonable CPI steps (although it starts to get jittery sooner than on a high-end optical sensor), and I couldn't detect any unwanted angle snapping or sensor lens rattle either.

CPI Divergence

CPI divergence is rather funky and follows the same pattern as with the other 3327-equipped mice I've tested before. It starts in the positive region, flips at around 2,000 CPI, and starts to go negative. While definitely interesting, it's not an issue in my book.

Perfect Control Speed

Perfect control speed (or PCS for short) is high on this sensor; the nominal 220 IPS translates to about 5.6 m/s. There is pretty much no way of hitting such a high value with regular use, so this sensor won't spin out if you land a huge swipe in-game. As you can see on the graphs, I never come close during synthetic testing on a huge mouse pad.

Speed Related Accuracy Variance

This test shows the sensor's accuracy at different speeds. You can see me doing a fast swipe to the right before I slowly slide the mouse back to its original position. There is pretty much no acceleration or deceleration here, or if there is any, it's due to human error.

Polling Rate & Stability

All polling rate values are nice and stable, without any suspicious outliers or periodic drops.

Input Lag & Smoothing

There is no measurable smoothing or any other delay until approximately 4,500 CPI, where some smoothing kicks in, resulting in approximately 1 ms of input lag, which increases to about 1.5-2 ms by the time it reaches the maximum resolution. For any serious gaming, I'd highly advise staying below the smoothed values.

Click Latency

Click latency is roughly 5.8 ms when compared to the SteelSeries Ikari, which is considered as the baseline with 0 ms. The data comes from this thread and my own testings. Testing was done with a Logitech G203 and the M55, using qsxcv's program.