Might be interesting to have an output from nvidia-smi while the GPU is still working to see if autoboost is available and enabled. Then maybe disable it and see if the GPU is still falling off the bus.
AFAIK there’s no way to set the GPU to minimum performance thus limiting maximum power draw. There’s a feature request somewhere though.
Edit: seems frequency manipulation can be achieved using CoolBits:
[url]Linux Hardware Reviews & Performance Benchmarks, Open-Source News - Phoronix