Writers such as A. Dumas (or rather his first anonymous translator) or A.C. Doyle do not use the construction "Such a big thing", but prefer "So big a thing" instead; 'such' appears only in the contexts where the construction with "so" is impossible. I have found somebody's opinion that using 'so' in this way is common in informal American English, and in the formal language is completely incorrect - but is this really so? Do I run the risk of sounding American if I use the construction?
I know that modern language doesn't need 'so big a thing' at all, I'm just curious whether it can be used without sounding American. It's hard to find anything about the topic in grammar books.
You will hear it used in British English too, so it doesn't sound exclusively American to my ears.