Further update - pretty sure I fixed this now. Several play-throughs of the MIG-29 landing without a single crash even on HIGH detail setting. Still getting the texture not found error:
2021-12-30 11:32:35.474 ERROR_ONCE DX11BACKEND: texture 'mi_8_tex_spec' not found. Asked from ''
But the game runs fine, with the odd transient framerate dip for 1 sec or so.
Made two changes that seem to have fixed this:
1) Further drop in GFX clock and voltage to a max of 1800 MHz and 975 mV (with aggressive cooling etc).
2) Enabling Radeon Chill FPS limiter (setting to min 30 max 100 FPS). Got one isolated crash without this; enabling it stopped crashes altogether (as far as I can tell anyway).
Answer was definitely clock/voltage on the 5700XT though. Log file attached if anyone cares to dig through.
Thanks for all your help.
Btw - any reason DCS is so sensitive to GPU clock/voltage? It's by far not the most demanding game I play graphically, but this is the only game that crashes.
dcs.log
Trubert's post in Constant hard crash to black screen, ERROR_ONCE DX11BACKEND was marked as the answer