Core clock is adjusted based on voltage + load. At idle, (assuming lower p states disabled,) you will see core clock at/near what you set. While mining, it will depend on the miner load signature - some algos will tax the core more than others, causing more of a clock throttle if you're significantly undervolted. This is all independent of other state settings (i.e. it is not related to P3.) Also, this only happens when ACG is engaged, which *should* only be for P5,6,7. In linux, you can step down to P4 to avoid this throttling, while in Windows, I have been unsuccessful in such attempts.
Generally I agree. However core freq throttling is also dependent what core voltage you set even if the card is in idle state.
When I was mining CNv8 ( which is not so core intensive algo) I set 1.100V because I could not get 1660Mhz on the core. Than my P7 state was set @ 1750Mhz (defult for LC). On this algo I was at 180W. On idle (no miner load) clock was as I set 1750Mhz.
On Lyra2rev3 core power is the main issue so on my settings I have 0.950V on load @ 1500Mhz and 1.000V @1600Mhz on idle. And that is with P7 set @ 1700Mmhz.
So Vega is throttling even on idle if you set very low core voltage.
I always use my Vegas with only P7 enable. I found that more stable when some network problems or pool problems occurs.
All above is more like a guide how to set your Vega, not a ready recipe.
I can't speak definitively to lyra2rev3 performance, as i have yet to benchmark, but with every other algo i've run, i've found Vegas to become increasingly inefficient above 1400Mhz (actual) / ~175w (at the wall.) If you're just out for raw production, and don't care about heat or the lifespan of the GPUs, then mine away at 225w or wherever you're at. Otherwise, you might want to check your hash/watt on some lower settings and compare (i usually find an 'actual' core speed of ~1300-1400Mhz to be a good spot for other algos.)
Since the biggest degradation of silicon IC's, especially for HBM, is temperature I use water to cool down that power hungry card. I have 38*C on the core and HBM under full 218W load.
Try that on air.
Using liquid cooling I also have higher efficiency but in my case this is completely irrelevant.
