if your getting crashes/hangs your pushing too hard with the clocks vs voltages

you can adjust in overdrivent while minning. start at 1200/900 and work your way up to 1466/960... with the memory you can go upto to 1105/910 (clock/voltage)

it depends on the individual card - silicon lottery

if your only getting 1400hs  you need to enable/disable each card... you can use device manager or much better is to use a devcon script.. if your getting crashes when enable or disable cards check the riser usb, power and pcie cables for that card

use the onboard video connector and virtual memory needs to be 10gb per card

using castxmr you should easily get 1900+ per card