On the 'relaxed formal shirt' topic:
Shirts with 1 or 2 studs are designed to stay 'closed' because they were properly starched to be like cardboard. I've come to only wear this sort of shirt (with separate collar) with evening dress, whether black or white tie. I've one shirt with 3 studs and a marcella front, which can be worn unstarched. Having become accustomed to the clean lines of an uncrumpled starched shirt, I no longer wear this. Sometimes this is marketed by shirtmakers as a "semi-stiff front shirt". That is because there are two layers of cloth for the bib, so it's naturally slightly thicker and less soft even if unstarched. Needless to say, it always looked better starched, but not as simple and elegant as a plain-front fully starched shirt. Shirts with 4 or more studs are designed to stay closed despite: (i) a lack of starch; and (ii) a low waistband. I don't think an evening shirt can ever appear elegant if it's worn with low-slung trousers, and I'd anticipate most readers here would agree.
I'm unsure that your project for this evening shirt would lead to an elegant conclusion. If you don't like having a bib on an evening shirt on the basis that it's exposed with your coat off, do you also also object to braces for the same reason? If you're not wearing braces with evening dress, aren't you already tending towards a lower waistband and a compromised trouser fit?
I agree that a stiff collar, stiff shirt, waistcoat etc can look, and in reality does often look, very awkward and over-formal. However, in my experience, that's caused because it's ill-fitting. I frequently see stiff collars worn 2 sizes too large, for instance. When the whole ensemble is closely-fitting and well tailored, I don't think it necessarily looks like outmoded costume, and it is in my view much more elegant, and so is to be preferred.
As an illustration, doesn't this clip show the most formal black tie as relaxed and informal (
http://www.youtube.com/watch?v=y6R5cXxxM8M) ? I think it does. And it looks, to my eye, rather better than this, the modern version at its best (
http://www.jamesbondsuits.com/blog/wp-c ... /10/24.jpg). Whether the 1920/30s version of black tie is costume or contemporary elegance, I think, depends in a large part on how well it is executed, and which will directly influence whether you're comfortable in it. I'd add that a waistcoat looks perfectly fine with a jacket off, if tailored so your shirt isn't hanging out anywhere. So I'd argue that the best option for an evening shirt, is still the most formal option, and the one that best suits being bespoken.
If you do accept that times have changed irreversibly, then arguably the best option is a simple plain white in a fabric thick enough to be properly opaque, even when warm and/or dancing. Pleats have no been always in fashion - a plain-front has been always fashionable for well over 100 years, and I think simplicity is better. I'd avoid "party shirts". They look rather teenage and attention-seeking to me.
Oddly, I think that the "stroller" is now definitely costume, and I wouldn't try it. This despite it being accepted as being more 'informal'. I wouldn't wish to be taken for a porter. Nor would I wish to look like I'd been to the Mason's Hall, which is near to the law courts (it's a bit of a members' uniform, from the outside perspective). Still less would I wish to look like a QC in a sleeved waistcoat, or someone trying to look like a QC. I've only seen 1 stroller in court in my time at the bar, and that more than 150 miles from London. Of all the sensible 20th century fashions one could pick, it's just about the only one that I wouldn't risk at work, at least not in a legal environment.
