Since I followed this thread closely up until purchasing my A64 system, I guess I should share my own results. I built my new computer last Thursday. My A8N-E came with the updated Asus hsf, but it runs at over 5000rpm and is still too loud in my opinion (although much better than the first version).
I installed the Zalman NB47J immediately and then ran 6.5 hours of memtest8+ as soon as I powered on the computer for the first time. The NB47J got very hot, but the test passed and I could keep my finger on it, so I proceeded with the build. Everything went well. I ran benchmarks, 24 hours straight of Prime95's torture test, I beat Half-Life 2, and I played a few hours of UT2k4. It's been on for about 4 days straight.
While the NB47J does get very hot, it's no hotter than the Asus's stock heatsink got. That heatsink is designed very poorly and the fan is merely making up for the poor design. Judging by how hot my finger feels, I'm betting the chip is running at about 60-65C. The system is clearly stable with the NB47J even in 75-80F ambient temperatures in a Sonata II, which isn't designed for high airflow. Let's also not forget that Gigabyte sells a few of their nF4 boards with passive coolers. Therefore, a good heatsink should be enough even though the nF4 runs incredibly hot.
System specifications:
Asus A8N-E w/NB47J
Athlon 64 3200+ Venice
Thermalright XP-90 w/Panaflo L1BX
Corsair 2x1GB TWINX2048-3200C2PT
BBA Radeon X800 XL 256MB
Sound Blaster Audigy 2 ZS
Western Digital 74gb Raptor
Black NEC 3520A 16x DVD+/-RW
Black Lite-On 52x32x52x16 Combo Drive
Antec Sonata II + Antec 38CFM front 120mm fan
Black Rounded IDE Cables
Enermax 485W Noisetaker ATX 2.0
Current motherboard sensor readings with an ambient temperature of about 72F:
CPU: 34C
Motherboard: 29C
Aux: 35C
Hard Drive: 35C
CPU fan rpm: ~875-900rpm
It's basically idling right now. After hours of gaming, everything rises by about 4-5C, except for the CPU, which peaks at about 43-45C.
I posted a few of these pictures in other threads, but here are some shots of my NB47J mod:
I posted this in one of the Sonata II threads:
The stock duct mount can also hold any fan you want. I tried it and it cooled down the northbridge and GPU significantly, but ended up increasing hard drive, CPU, and "motherboard" temperatures. I also assume that increased the PSU temp as well. Anyway, I did all of my stress testing without this 3rd 120mm fan, so I only tried it out for about an hour. I decided to put it in the closet and only use it if I need to later. For now, my computer has proven to be rock solid with only the NB47J.