Koniakki

I don't remember to have seen anything on the HC 780 but as I saw elsewhere Classy 780 member are way more than happy with them and their OC are simply.. well stunning. OP I came from a 1176/7Ghz+ 690 to a 1254/7Ghz 780. So you might wanna read the post I made in another thread below. http://forum.techinferno.com/nvidia-video-cards/4760-upgrade-no.html Anything minus 780/titan SLI and Classy/Lightning 780 is a downgrade gaming wise from a 690. But I can't really recommend the 690 anymore. I would take a Classy 780 anyday over it.

I posted a detailed thought below in another thread about the same thing. http://forum.techinferno.com/nvidia-video-cards/4760-upgrade-no.html

SLI sometimes don't run at same clocks. Even my previous 690 1st gpu was running 13Mhz lower than the second(1150 vs 1163). So its not uncommon. And 1006 vs 1019 power draw wise is negligible. Also as you said at "stock" 954 everything seems fine and only when the cards are pushed this happens. So can try this. Take out the 2nd card. Leave the 1st inside and since the shutdown happens when they run above stock, OC the 1st card to 1100-1150mhs/+350mem if possible and run Valley/Heaven/3DMark and play a couple games for like 10-20min each. If it passes all the above at 1110-1150/+350mem remove it and repeat the same for the 2nd one. If both cards passes those tests at those clocks let us know since the culprit might be something else.. P.S: Try using a stable CPU/Ram overclock if you have oc'ed the CPU/Ram. Or just leave CPU/Ram at stock and if possible bios settings at default/optimized.

1st 690 SLI(quad gpus) is actually not recommended by many. Too much horsepower, little vram. Its like having the power of the Sun and lighting a 100w bulb. Not the best reference but you get the idea.. Coming from a good 690@1176/1800 down to a 780@1254/1752 in gaming the difference is a lot more than reviews and benchmarks shows. As I said elsewhere, I love my 780 but purely for gaming the 690 is a lot more powerful. No doubt the 690 culprit is the vram and the throttling but FC3@4K ultra settings/no AA with my 780 uses 1750mb vram(avg 45-50fps), I can say the 690 has still a lot of life in it. So assuming someone doesn't go over-board with AA its 690>780. No back to the OP's situation. Imho I would just find another dirt cheap 670, oced if possible both cards to 1250mhz and call it a day. Best bang for buck and I'm inclinded to say performance wise too. BUT, if you can sell you current 670 and add the price you would had paid for that 2nd 670 and with that total you can find a used 690 for the same or just a bit more($50-$80), then go for it just for the better hardware sli that the 690 provides. Otherwise SLI 670 beats 780 anyday and also might beat/match a 690 since most don't OC well. So my vote is go for 670 SLI and wait until Maxwell and see what those bring in the table. P.S: Don't forget AMD's r9-290/x if you don't mind waiting or going Red. They might surprise us and I would definitely recommend them over a 780 and even a 690 if the reviews favor them well. Also 4GB vram seems really sweet too!

Performance and gaming wise, even a 1400mhz 780 cant touch those classy 770's in SLI. Not even by a long shot. I have a 1254Mhz/7Ghz 780 Jetstream and purely from gaming/money perspective the 770's are the way to go. And I came from a 1175/1800 690. Not the wisest choice but the fastest one.