It took longer, but 250/0750 also a dead end. Over 500 first hour, then down. After 3h down to 485 average, 458 last hour on the pool. All "o" on the chips and only 1 HW. Dropping to 243/0750 for the next run.
243/0750 also a dead end, dropped to 4h running average of 471, with last hour on the pool at 449. Trying 237/0750.
I also started playing with the slowest of the others (225 for 453, no voltage change). Trying 250/0750, and so far 2 hours in it is rock solid at the expected 504. Not going to count those chickens, will see what it looks like tomorrow.