Greece
London to Athens
1,508 miles - roughly 3.75 hours in the air. You'll fly into ATH.
So - is the upgrade worth it on this one?
The marginal case. 3.75 hours is long enough that a cramped seat genuinely wears on you, short enough that business-class prices can be hard to justify. Premium economy is usually the interesting comparison here - and whether any of it is worth it comes down to the fare gap on your dates, which changes daily.
Ask Aster with your dates and it compares live fares in economy, premium economy, business and first side by side - including what the seat itself is actually like - and gives you a straight answer instead of a hunch.
What the seat is actually like
Most flight sites sell you a cabin name. Aster keeps a seat-intelligence library of real aircraft layouts across 25 carriers - so on this route it can tell you whether "business" means a private suite with a door or an older recliner, before you spend the difference. That distinction matters more on Athens than almost any other factor.