I recently bought some Bosch ship auger bits(I work for Bosch too). Bosch has two types,type I and type II. I talked to the Bosch marketing people and was told to get the Type I for cleaner holes. Type two are for going through staples and nails if you hit them, and while it does that, it won't leave as clean a hole due to it's more aggressive nature. So the type I 's are the way to go. I am new to timber framing too, so I don't have a lot of experience yet. I have no familiarity with Irwin bits.