Even at the default TDP of 38.5w (4 cards @ 154w), that's still dangerously close to the limit. Try to connect as few cards as possible to each power lead, or use a higher rated connector designed for more power, like the 6-pin or 8-pin PEG connectors.
I don't get why some are voluntarily going from 38.5 W to 65 W for maybe 10-15% higher kHash/s rates.
This kills Maxwells excellent power efficiency.... and apparently also PSU cable connectors.
After unlocking the TDP (and before catching fire), I was able to overclock a card to 1450MHz core/3900MHz memory, resulting in a hashrate for vanilla scrypt of 340kh/s, and still at a core temp of < 65°C.
65w is still exceptionally efficient. For me, it was to see how far I could push the card. Sometimes that means you'll burn through a card or a cable, but it's all in the name of science (or something like that). It's an interesting experiment nonetheless.
That said, one could damage their rigs even without bumping the power thresholds, and that's the point I had hoped to get across.