It is a bit of a gymkhana so I thought I post a progress report.
I first used an Enermax 280 (as exhaust) with the TRX40 and it was very bad. I think this unit was faulty, actually. I replaced it with a Corsair 280 and it was much better, but not enough to really use the 3970x passed base speed. So I put an Enermax 360 as intake, because that was the best possibility I could get fast enough in the present economy. It's about the same cooling performance as the Corsair 280. Albeit I have to say that by the time I got the Enermax 360, I was out of thermal grease, my order was still days away and what Enermax had bundled with their 360 was totally unserviceable, part liquid part solid. I had to remix it (while the computer was open, the radiator fixed...) It was a mess, I had of that grease everywhere.
So I now have that Enermax 360 as intake with a very bad grease and I can run about 90% of the 3970x (56 threads) at base speed (3.66) under 80C. That delivers about 600-650K point/day, that is about three time what I can get with the 7940x at full speed.
Tuesday, I should get some decent thermal grease. I'll see what that can achieve. And in a week or two a Corsair 360 should arrive. Using it as intake, maybe it will be sufficient for the 3970x. There's a good chance I think because I'm now using the same Corsair 280 that was cooling the 7940x as exhaust (some 70C at 100% load) in a new case, this time as intake, otherwise with the same material (same MB and GPus, just less disks and RAM) and it delivers a much better performance in that configuration (<60C at 100% load). There's hope!
EDIT: The grease came today already. It's a 10C difference! Thermal Grizzly Kryonaut (12.50W/m K).