I have a 2019 G20 320i Msport I bought a few years ago, second hand, BMW main dealer AUC. At the time it only had 24k miles on it. Was also looking at a 330e as well for the same reasons you mention - lots available, attractive with more performance. I had an 3ltr diesel Audi A4 in Germany (around 260hp), and was faffing around for ages working out if i should get a 330e or 320 over here almost purely on performance merits, but also range. In the UK, honestly I don't need anything more. The 320i is perfectly fine for all types of driving and has enough umph for this country the vast majority of drives. Economy - i get around 46mpg mixed motorway and A roads. Long motorway journeys is in low 50s. Over 500 miles in a tank. I've taken it over to Germany 4 times so far and it'll sit perfectly fine at 170>180 kmh (105 > 110mph) for as long as. Anything over that and it sucks fuel (like most cars do) and gets uncomfortable tbh. Add in 3 passengers and luggage though and it will start to feel a bit sluggish at times.
What I really wanted was a 330i, but there were none available at the time.. just tons of 330e's.