I am constantly amazed at the stuff you post as if its fact on here at times.
The E61 530i N53 has 272bhp, it is very much powerful enough. It's also the most fuel efficient BMW petrol six ever produced. It has a stratified direct injection system (which is why it was only available in Europe) for fuel economy benefits of up to 20% over the previous N52 engine. I once did a 150 mile A road trip (hills, overtakes, etc) in an N53 engined E60 and averaged 39mpg! For context my 530d does about 42 on the same trip. On a Motorway trip it could easily top 40mpg.
Your 330i had a completely different engine, so not sure how thats relevant. Doubtless you'll explain you didn't realise but if you don't know much about these cars why dispense advice to people on them and tell people to avoid buying them?
You also didn't sell your 330i because it wasn't 'quick or economical' because you replaced it with a car that is both much slower and more thirsty