One question very few people cared to spell out was WHAT STIFFNESS are we trying to improve? Spindle stiffness? or down tube/bb shell/chainstay stiffness? The 30 camp is focused on the former, and the (3)86/90 camp focuses on the latter.
I'd be interested in seeing some separate data on spindle deflection versus frame deflection.
Another very important feature of BSA is the self centering effect of threads, which give you much greater tolerance than press-fit.
Valid points Elviento... but I still think the whole stiffness issue, or whatever the marketing people want to come up with to try to sell this, is a red herring. I think you realize, since you probably have more experience seeing the actual process in manufacture than anyone on this thread at this point, that building a molded frame around a perfectly aligned threaded bottom bracket shell presents manufacturing challenges and cost that are so easily avoided by, well... just leaving a big hole there and trying to make it round enough so that the end user can press some cups in after the fact and call it good. Plus, without that big heavy shell in there, our frames will weigh less too... and that sells. Oh, and for those frames that are bit out of tolerance, just tell them to Loctite the hell out of it till it stops. Not our problem.
As to the threads, they do provide some self centering by design, and with the introduction of outboard bearings in threaded bottom bracket, I can't stress enough how important it is to properly face the BB shell once again, just like the old days. Install a Campy Super Record Cult crank into a properly faced threaded BB shell, and that thing spins like nothing else. Don't face it, and well... you get what you put into it.
Campy's attempt at adapting to the pressfit bb shells had some issues, largely due to the finely machined alloy cups which might seem like a good thing. Until you try to press them into frames that have been manufactured to tolerances much less than the matching cups. Creak creak creak. We'll see how Campy's new cranks for the new "standards" fare in the coming year I suppose.
But given the choice, I would still opt for the only "standard" that we still have and that can be legitimately labeled a "standard",... the BSA 68mm threaded shell. Widening everything down there presents some challenges too, with crank profiles, Q-factors, and I'm sure some other stuff. The whole affair has just created a minefield of confusion and problems that just simply weren't there before all of these "innovations" started.
Let's be clear, the move towards pressed in bottom brackets has much more to do with ease of manufacture and cost to produce than providing any real benefit to the rider. I suppose if they eventually get it right, and really do solve all the tolerance and compatibility issues then it won't really matter, but so far... they haven't.
Is that more than 2 cents worth... I wasn't counting.