Thanks, lecap, as usual your expert knowledge and advice is much valued.
And, no, my riding style and ability don't justify a 690. In fact, I've just sold the one I had because it was too "hairy" for me and couldn't sensibly carry luggage. But, the KTM's harsh suspension (it felt like an unsprung 1945 Ariel) did make me wonder if my DR should have beefier front springs.
However, it turns out that the puncture I got yesterday was not a snake bite - something stabbed me in the sidewall.
And I've taken note of your previous comments about changing the fork oil viscosity and, when this was suggested by my mechanic, I said, "No, keep it standard".
I'm taking Chopperpilot's advice and putting in a 4mm tube and a new Pirelli tyre. (The dealer says the Pirelli tyre has steel reinforcing as distinct from other makes which have fabric - I don't know if this is true?)