I go to the opera here at least twice or thrice a year, and I usually wear my dinner jacket (SB, peak lapels). I have a vintage Pierre Cardin that I scored off eBay for €20 that miraculously fit me like a glove wiithout any alterations at all. Of course, I'm fussy, so I had the sleeves trimmed and shortened and the waist suppressed a tad. Mind you, I could try on 50 jackets my size at a shop, and if I'm lucky, two might fit me correctly. The fact that this eBay bargain fit me so well must have been destiny.
If I want to get super dressed up, but not go "all the way" with the dinner jacket, then I'll swap it out for my velvet tourmaline jacket and keep everything else the same: tux trousers, black barathea bow tie, vest or cummerbund.
Neither outfit ever fails to elicit compliments.