Firstly - when you do put your 540 up for sale let me know!!! I've been on the look out for one but I haven't got the heart to sell mine for now after all the work I've done so far...
That's fair comment on the prognosis, a 335i is in a league of it's own! But I would always give any car's I'm going to buy a bit of a test (not thrash it but you know what I mean a bit of WOT), becasue you don't want to be buying a 5 litre monster and have to drive it round like a micra because it can't take any throttle without bursting something! Although it would still look pretty...