I think I may be having an issue with one of the vid cards, I'm afraid. I've installed SpeedFan to monitor temps, and one of the video cards is fluctuating between 112° and 126° F, and the cooling fans for that card are fluctuating right along with it, ranging from 54% and 100%. Now it's been a while since I did any overclocking and had to monitor temps (and I'm not overclocking now, but the info is still important at this point), so I can't recall what the "functional limit" is for GPU temps, so I'm asking, how hot is too hot?

Blimey Dave you have given me the temps in Fahrenheit, honestly means nothing to me, some conversion will be needed. 

That is one of the main problems with two card though, you can't cool the top card because there is so little room for air flow.

OK, I had a little look-up for your card to make sure I was still up-to-date, and as yet nothing has changed regarding safe temps and AMD graphics cards.

You want to try to keep the cards GPU to a maximum temperature of around 70C to 75C, if you see the temps hitting 80C it is too hot. 


GPU's do run much hotter than CPU's but I assure you 70C is fine for an AMD GPU.   

Then I don't seem to have anything to worry about, and just need to change some limits. Sorry about my failure to convert. Wasn't thinking. The max temp is right around 51-52°C, so I'm ok with that.

The Northbridge is also running around 50°C, but that's the upper limit, and it wasn't tossing out warnings.

You are well within the limits for your GPU's, no probs. 

The Northbridge temp is a little on the warm side but not in a danger area, I find a small fun blowing in the side of the case and directly onto the mobo reduces it quite nicely.   

Ther Northbridge has it's own fan, but it's buried below the GPU's, with no real airflow potential. I'm going to order another 120mm fan to mount on the side cover, which will blow straight on it, and hopefully that will take care of it.

if that does not work remove the nothbridge fan and heatsink leaving room for a nice water-cooled setup   
hmmm maybe even water cooled gpu's can even be added in, you have plenty of room 

Actually, for that sort of thing I don't have the room. There's less than an eighth of an inch between the NB fan (which is a low profile unit) and the "bottom" edges of the vid cards. And while there's a PCIE slot's width of space between vid cards, the Audio/LAN card takes up roughly a third of that, and it can't be put anywhere else.

you could always just water cool the gpu's which would allow for more airflow over the northbridge