Last two days have shown that allowing for texture rescaling (the "small" setting, which is, I believe, a moderate step-down) helps a lot. While in Flotsam, now I'm crashing not more often than once an hour, usually when the cell is reloaded upon crossing a gate or when switchig to/from UI screens.
From time to time (Flotsam again!) the said UI screens lose the background:, which becomes either transparent or totally black. This is a warning of some menory problems; time to save, exit, and restart (if not: KABOOM!).
Interesting if other large cities will suffer from the same problem. I should see that tomorrow.