Well, I installed the Thermaltake Frio yesterday. The northbridge heat sink actually ended up not being a problem at all. I could have positioned the cooler horizontally or vertically and it wouldn't have gotten in the way. The mosfet heat sink is the only thing that caused trouble. I ended up positioning the Frio horizontally (blowing from front to back) because to position it vertically would have required a little bit of Dremel work on one of the plastic fan mounts of the cooler so it could clear that mosfet heat sink. Here are a few pictures:
Positioned vertically, here's the contact with the mosfet heat sink.
Also positioned vertically, just barely misses the memory.
Positioned horizontally, doesn't come close to the memory or NB heat sink.
And finally, here it is fully screwed in.
Oh and what's the deal with the hole in the antec 900 behind the motherboard conveniently positioned so you can access TWO of the four CPU cooler holes. Pain in the ***. Here's hoping I installed it correctly and won't have to reseat it any time soon.
EDIT: Oh, and in addition, I sat the motherboard in the case and positioned the Frio both ways. It doesn't appear
to get in the way of the side panel fan.