I have a roofing job coming up, using steel sheets onto wooden purlins with wood teks. Previously I have used a standard cordless drill - does the job, but initial hole through the tin is difficult. Would an impact driver be better? There seem to be two types - 6mm hex drive or 1/2 inch socket drive - which do I need? Assuming the socket drive is better suited for workshop use (but it would be more useful afterwards). The small hex drive wouldn't get used for any other job.