I now have the ability to switch off Captcha, so I'm going to try this to see if it makes any difference to the ongoing problems with comments and timeouts and so on. Let me know if it helps.
Impressions of switching off captcha seem to have been favourable, but unfortunately I'm not going to be able to cope with the volumes of spam. I've had to switch it back on again.
Advice seems to be to avoid using preview and edit repeatedly.