Fly sizes, line weights, and leaders

I'm interested in the range of fly sizes different fly-fishing equipment can handle, and the degree to which you can influence this by leader design.

Let's take a well-known dry fly, say the Adams, in different sizes, and three fly-fishing sets: 6wt, 4wt and 2wt. Each set is rigged with a "standard" floating DT line. Let's also assume that there's no wind.

Now the question is: for each of the line weights, what sizes of the
Adams can the fisherman comfortably fish with, assuming that he will be fishing within 40 feet? Moreover, if the fisherman is making the leaders himself, can he increase the fly size range by using thicker tippets? One advice on how to select the tippet diameter is given here:

Well?

Due mainly to my own ignorance, I won't speculate on the exact size of the fly one can manage with a particular line weight. OTOH, I will say that thicker tippet should help with bigger flies in most instances.
If you need a thicker leader/tippet combination than is commercially available, making your own would be a reasonable solution.

If nothing else, the lighter tippet usually associated with lighter lines will twist once the fly gets too big. If you haven't had first hand experience with this phenomenon (I have) then you should read any

Creek throwing a big Gray Fox (#12?) with a 4wt

Shipps> Buy a copy of The Orvis Fly-Fishing Guide, it's in there. Now
Shipps> go fishing and don't sweat the small stuff.

Yep, I guess noone in their right mind would be pondering over such questions in the summertime. But I can't go fishing since a) I'm sick with the flu and b) have too much work to do. So nothing else I can do that to be interested in the small stuff, and sweat (a lot).

Seriously, though, are the questions that I posed really answered in the Orvis guide? I have a couple of fly-fishing books, but haven't seen this issue really covered, especially the thing about how self-tied leaders might change the situation.