I flashed back to the stable 4.7.0 firmware meaning the non-op24 version and my SQM is back to normal. Setting 1000Mbps results in 950Mbps with bufferbloat under control.
To be clear, with the same configuration the SQM performance limit with hardware offloading disabled is:
4.7.0 stable = 950Mbps or more
4.7.0-op24 = 450Mbps (600Mbps with software offloading enabled)
Hopefully the team can get this fixed for the next release of op24.