Hi Edd,
Thanks for sharing and the suggestion. We are keep on trying to offer more info for different requirement / applications.
Refer to the two things that you are going to do, they are all reasonable. Using polling mode to read the data may be the most easy way if your MCU timer is more accurate.
I just would like to share more insight:
1. ADXL362 support external clock and also support synchronized acceleration sampling to an external trigger. If clock deviation is the key to you. You can also consider to use ADXL362 and using the external clock.
2. If you want to do the integrating to get the velocity, I think the error caused by noise and tilt variation (tilt and acceleration due to motion are indistinguishable by the accelerometer) over the integration period is more than the error caused by the clock deviation.
BR
Neil