personally i would not change for another E34 unless it was significantly better condition than mine.I cant comment on the 540 auto but i drove a couple of 540 six speeds(2 e 34 and a e39)The power and civility is head and shoulders above the 535 5 spd but the brakes and steering werent.Even after the e39 540 six speed the 535 still made me smile,and it felt right...i was afraid it would feel old...but it didnt!a 540 six speed in either model would probably use slightly LESS petrol than the 535,not sure how the auto would affect that