There are issues with dynamic power states on both AMD and NVIDIA parts to this day. In general, I'd prefer voltages to be set for absolute worst case scenarios and the cooling to match, rather than trying to squeeze every iota of performance out of a given power envelope, and risk slipping into instability.
I ran the PT1 firmware on my reference Hawaii parts because that solved essentially all performance/stability issues, then I set a fan profile to handle the heat.
With my non-reference parts, I've hand tweaked the firmware for each sample (not model, but each individual card), to ensure there are zero hardware related crashes and zero EDC errors with the clocks I'm using, at the lowest voltages and quietest fan curves practical for worst case loads.
The problem with the reference Hawaii parts was the cooler. Sure they could have spent more time and effort probably failing to save enough power with more complex DPM states and better error checking, but they could have spend three more dollars a card to put an adequate cooler on it and achieved the same practical result.
I'm not familar with the ATi Tray Tools feature you mention, as I haven't used ATi Tray Tools in years. I'm not even sure it supports recent GPUs.
...rightful liberty is unobstructed action according to our will within limits drawn around us by the equal rights of others. I do not add 'within the limits of the law,' because law is often but the tyrant's will, and always so when it violates the right of an individual. -- Thomas Jefferson