The problem was Intel's default stock chip cooler system, which is marginal if you want to run full out for an extended period. Marginal, at least, if you don't implement their recommended side ducting system.
I wanted to get this problem solved so that I will not have to watch my operating temperatures so closely while running BOINC or other intensive applications. After some research, I ordered the Cooler Master V8, a large heat pipe / radiator / fan system that fills up my computer case very nicely. (Leaving a little room, but not much, for hooking up the wiring afterward. This kind of assembly is not for everyone.)
The following photo gives an idea of the scale and airflow. The flow from the cooler's embedded fan conveniently goes directly to the case's rear exhaust fan.
The bulk of the radiator system really does take up nearly all the volume above the CPU, but fortunately there were no mechanical interferences on my Gigabyte EX58-UD4P motherboard or RAM. The whole thing just fits in the Antec case without trouble. It does weigh almost 900 g (about 2 pounds). While the motherboard mounting seems fairly secure, I am sure that my computer will not fare too well if dropped on a concrete floor.
The quick before and after comparison, with my undervolted i7 (Vcore=1.01250 V):
Temperatures are (Tgpu, Tcore, Tamb, Tchip in deg. C)
8 threads of BOINC code (Proteome Folding Project)
Before: 48, 80, 39, 75
After: 45, 52, 36, 45
The final (chip) number is the best one to focus on. An improvement of 30C is a lot more than I had expected, but I will accept it! This is all with the cooler fan running at 1767 rpm. It will run up to about 1970 rpm, but that noticeably adds to the noise level. The higher speed does not lower the operating temperature by much. We might need to speed up the case's exhaust fan if we care about cooling more than noise. (I don't!)
I should emphasize that "normal" interactive computer operations would be much less than the 100% load we are discussing here, so that even the stock Intel cooler would be fine. On the other hand, if you are spending the money for the i7 system, why wouldn't you want to run it full blast?
According to my (perplexed) intuition, having read much of the Intel literature, it should be fine to run at a chip temperature of 60 C, at least. So there is a lot of headroom to explore overclocking with higher core voltages.