Open Fronted Doublets

[CMcG]

I'm interested to know what the rabble has to say about open fronted doublets, specifically the Sheriffmuir vs. the Regulation? Pictures are, of course, most welcome. And yes, I've searched through some older threads but would still like to clarify a bit more...

It seems like these are the two generally available styles that could be worn with a waistcoat. Are there other non-bespoke options?

I've read that doublets (in general) can be worn for both black or white tie. Does this apply universally or are these open fronted doublets more germane to only one level of formality?

What different ways are there to wear a Regulation, Sheriffmuir, or other open fronted doublet at different levels of formality (re: neck wear, shirt, waistcoat/vest, accessories, etc)?

My birthday is coming and I'm considering asking a few people to chip in on a used doublet. Any suggestions (other than eBay) about where I might find one? I'm a fairly standard 38R.