I made 4 or 5 changes at once so I'm not exactly sure which alteration fixed things for me; I saw advice on a forum post about this game crashing that said essentially, you might think you've got a stable OC, but then a game can push it and breach your 'safe' levels. I switched off my OCing, and touch wood have had no crashes since; I turned off ray tracing also, but have since turned that back on and again managed to play a complete session and exit to windows. Other things I changed, in case someone else is reading this looking for help:

manually set the page file size for the drive it's installed on (25gb)
turned off v-sync in game options, used the 'fast' setting on Nvidia Control Panel
set 'Anti-alias' to 'off' in Nvidia Control Panel

Like you say, optimising any program for PC is very difficult... so I'm always willing to give some benefit of the doubt with games that push the envelope. This has probably been the least-pro experience since the launch of No Man's Sky (which as it goes, is imo an excellent game now), AAA studios should be aiminig higher than tiny startups when it comes to stability!