Yep, seems like it's been said. 2.5" to 3" for the main body or bulk of an intruder style fly for normal conditions with the longer more swimmy materials extending another inch and change beyond that. For big or dirty water, a 4.5" or larger fly isn't overkill and it is good to have some of those in your arsenal. For low and clear, don't be afraid to drop down to the LBF (little black fly, 1.5" to 2") as I have seen it makes the difference on what could have otherwise been fishless days.

I am not afraid to fish a #4 for big fish in the right conditions and have landed more than one 20lb steelhead on them. That having been said I fish 2's most of the time, 1's in heavier water.

Nice quiver there metaladdiction. If it is not peach, pink or orange, it should be black