So update on the 770 hitting the infinite reboot loop, requiring a reflash to gain normal operation (8th time already in 2 weeks).
Managed to get it to fail with latest 3.2006.49-2 fresh installed, and only VNCViewer 0.6 installed. About a day after installing VNCViewer, read RSS feeds (added nothing new), retrieved emails (1.6MB), I noticed the amount of Free Storage dropped from the typical 50+MB to ~29MB. So 20+MB got consumed somehow, and the Memory app struggled to display it. The Memory In Use kept creeping up past 12MB/25%, but never really completed (was awfully slow in terms of progress). The numbers didn't seem to add up as they had done earlier (when at 50+MB free). So I pressed the power button, selected Switch Off, waited a while, hit the power button and infinite reboot as I have come to expect. So this removed Maemomapper from the suspect list and left:-

VNC Viewer 0.6
Default RSS feeds
IMAP4 Email configuration

Now I had Maemo mapper, RSS feeds, email running fine for a few days, and then added VNC Viewer 0.6 and it died within a few hours.

I think my next test is not to install *any* apps and see if it dies with a default config.
Suggestions? Conclusions?