Oh believe me, I accepted it about 3 years ago when I bought my first 4.2. I mention it mainly because most people who are used to the standard 1.8T A4 can't believe just how thirsty an engine the 4.2 really is. That first 82L fill (in my case, I know your tank is only 55L) and realization that you only got 300km for your $140 comes as a mighty shock to most
To expand on your S4 4.2L comment, that specific variant is a brutally expensive engine to maintain/repair if something goes wrong. Timing chains are on the back so forget about an "affordable" $1700 timing belt service, doing the timing chains on that engine is roughly a $3500 service because the engine needs to be pulled. In fact pretty much every maintenance job starts with "Remove engine" as it's first step. If something does go wrong, you're usually looking at replacing the engine altogether. A buddy of mine in Edmonton just finished doing it on his Dad's 2005.5 Avant (Mike's old S4). Crate engine was about $17K plus install; he ended up finding a rebuildable core in Calgary, ordering all the maintenance and rebuild items online, then had a local shop do the rebuild. He and his dad installed themselves to save on shop labour and it ended up being a steal at ~ $13,000 all in.
As much fun as my engine would be in a car that weighs a good 700 - 800lbs less, the 2.7T is the much much better and more sensible swap option for a B5. It would be interesting to see what the balance would be like with a 4.2 in a B5, the C5 and B6 V8's all used a lot of aluminium panels, subframes and suspension pieces to help keep the weigh down and to keep the car as neutral as possible, I have a feeling the B5 would be quite nose heavy without that weight reduction.