Remember to keep the bit very sharp and drill slowly allowing the bit to stay cool. Heat and pressure will result in a blown blank, especially with a big bit.
For these lengths the shorter the better. Personally I purchased a 14,75mm HSS extra short drill here in Brussels and I'm more than happy. A lot less vibration compared to a long 37/64" drill I used previously. Of course the price... (+/-US$40 :biggrin...