I’d be surprised if anyone can with confidence tell you the answer to that specific question, and quantify the respective downsides. It seems hard to see how someone could know the answer with confidence. I also imagine the difference is quite small, and I’d guess it might well depend on what else you have that day and on neighbouring ones, and you as a person. But what do I know…
Empathise with your point though. If you, say, want some white with your starter and red with your main, you have two open bottles on your hands, which is a lot of wine.
I often cool wines, then immediately on opening pour half the cold wine into a screw cap bottle to the brim and put in fridge, leaving the remaining half full bottle to warm up to serving temperature. The stored halves often keep well, and it’s not unusual for the wine to be better three or four days later. Indeed, I actually think that younger wines can keep surprisingly well like this. I’ve heard reports of people keeping them for well over a week.
As well as half bottles, I have 250ml bottles so can be quite flexible.
Though some wines, especially red Burgundy and older wines, don’t respond well.
I’ve faced your dilemma of a left-over 150ml. It can end up being consumed with cheese on top of half a bottle. The good thing about sending it to the mirepoix is that this temptation is gone. You can also freeze small amounts for cooking on other occasions, or turn into vinegar, of course.
A friend who drinks extremely expensive wines (£100 a bottle stuff, though I should say is humble, learned, and kind and generous with his remarkable wine and knowledge of it) once said of this dilemma “if you don’t want it all, just tip it down the sink”.
I shivered at the thought of Gaja slipping down the plughole. But in a way he’s right. Better to enjoy wine, really savour it and not have what you don’t actually want, or suffer for it. Though I wish I could fill my dinky screw caps from his kitchen!
The way I look at it is that a 150ml of a 12 quid wine is worth £2.40. Well if cooked with, let’s say it’s worth half as much. You’ve lost £1.20 of wine value but feel better in the morning. It’s not a bad trade really.
The downside I face is that storing half and third bottles tilts me towards younger, robust and cheaper wines. My Burgundy gets drunk less often even though I prefer it!