Ok, now that everyone has made fun of what they did not understand lets get back to the question. I think the main reason your bit broke is because it was "carbon steel". The least expensive bits are usually HSS which is much harder. HSS bits cut steel just fine but when it comes to wood you need carbide if you want it to last. If you need to use a straight bit then the best choice would be a solid carbide spiral up cut bit. These bits do a better job at removing debris than straight bits. 70 feet is quite a long run and should be done in sections allowing the bit to cool. Remember that heat kills even the best bits available.
Derek, if you have not tried one the "Cyclone lids" that fit either 5 gallon buckets or garbage cans are a great safety device to protect your dust collector. Using one of these devices in line changes your system into a two stage which captures most of the dust and debris. No more broken fan blades and the cans are easier to empty than the bags.
"Living in the D" (this means Detroit!)
"It's fine to disagree with other members as long as you respect their opinions"