I updated one of my Bitaxe Gamma 601s with an ice tower for a heatsink and a Noctua fan, and I also added a back fan. Both ASIC and VRM are running under 50 Celsius, so I think it's working OK.
One thing I've noticed is that most people are orienting their tower/fan left-right, whereas my setup is up/down (as pictured). I realize heat rises, but the issue I saw with the side-to-side orientation is that it at least appeared the tower wouldn't make full contact with the ASIC chip. Are you guys doing an extra step to get it to work?
Curious!