There are really, only about 3 major types of double-butted throughout frames, with minor variations on a theme. Tubes are typically characterized by the width unbutted / butted / unbutted, in the main tubes. Variations in lugs, fork crowns, and the rear triangle can change things, but the main tubes tell the main story :
9/6/9 - these are heavy frames, often called "Super Tourist" and used for load-bearing frames. The wall density is .9mm, .6mm, and .9mm. You might look at advert's for Thorn's 9/6/9 loaded touring frames in CyclingPlus (UK) for examples of these frames (ex: Thorn Nomad.) Also, Reynolds 531 ST (super tourist), and Reynolds 501, etc, are 9/6/9 frames, as are columbus Thron frames, usually.
8/5/8 - this is the classic Reynolds 531 frame (pre-1980 marketing name) or 531c (post-1980 marketing name) frame. In my opinion you can make it two ways. The first way is cheap : a low-cost brazed rear brake bridge, maybe with a washer brazed-on to support a caliper (ex: Raleigh competition). The second way is nice : reinforced or filet (paramount) rear brake bridge, and cutout in the bottom bracket to show that the builder cares about weight (ex: Raleigh pro, Colnago).
7/4/7 - this is a balls-out ultra-light, time-trial frame, or perhaps a small (19" or 20") high-end road racing frame. Examples include Reynolds 753 frames, 531p (professional) frames, SEKAI 5000 Superlight (actually 6/3/6 in the top tube, i believe), etc. The bike will have to have a very short wheelbase to reduce flex from the flimsy tubes. Today's 7/4/7 frames use newer air-hardened (853, true-temper OX) steels to get back some of the lost strength.
It doesn't really matter if your frame is made of chromoly (tange), mang-moly (531), stainless (953), niobium (columbus), or some other exotic steel alloy. Steel is steel and steel alloys have about the same mass per unit volume. So all 9/6/9 frames weigh about the same, all 8/5/8 frames weigh about 150g less, and all 7/4/7 frames about 150g even less, more or less.
However, there are many people that prefer the resilience and shock absorption of a mang-moly (classic 531) frame over the other formulations, with a similar following for classic Columbus tubing. I talked to a framebuilder in Joe Bell's shop at a ride last year, and he built himself a Tange Prestige (7/4/7) frame as an experiment, but he found after a few rides it was "too squirrely" and he put it aside, and once again rides Reynolds 531 exclusively.
- Don Gillies
San Diego, CA, USA