What method did you utilize to test ping spikes and stutter? I used the following guide for SQM and the following bufferbloat testing website:
openwrt.org
Is bufferbloat causing issues with your internet connection? Run this test to find out.
www.waveform.com
If i configured SQM Upload and Download speeds very close to the claimed 100Mbps, i would get stutters and spikes - however i got the most optimized results (after a lot of testing) @ 93Mbps.
Could you also share screenshots of your settings on the PTCL ONT and your router? I might want to try your way out.