The Davy Knot isn´t just for light tippet or small flies - rather it is a knot that must be matched appropriately from tippet size to wire guage of the hook. The knot architecture makes this a requirement. Basically you need to use common sense and use a tippet that is approximately the same diameter of the hook, with some leeway. I am on the mouth of the Amazon in Brazil right now as I check this; I´ve just spent the last three days landing piranha and peacock bass on the Xingu River, and I used the Davy Knot a lot.
In 20# test, on multiple occasions, the Davy Knot to hook connection outlasted a triple surgeons knot in the middle of the leader. Over and over this happened. Just be very sure to seat the knot securely with heavy tippet - use pliers to lock it in. It won´t come off.
Zach Matthews