I have been using the bosch self feed bits agree that the make light work of itI purchased the hole hawg. It is great, but only as good as the bits you use. Try the bosch self feed spade bits. They make light work of drilling joists.
Also found that the hole hawg doesn't use as much battery as a combi drill does drilling joists.
Powertoolsgb.co.uk currently selling it for 218 quid inc vat. I paid 250 for it so that's not bad deal.
Would definitely recommend it.