I have a F15 35i (N55) and a E70 48i (N62). I love them both but I would stick with the turbocharged straight 6 (N55) for reliability, imho. The N55 won't have that low, deep rumble but I have learned to appreciate the raspier sound of the N55. Also, if you buy the N55, you will probably have more in the budget for exhaust mods. I have been toying with the idea of
cut outs on mine. I already have a software tune on mine and it made a subtle increase in the tone / sound.
Good luck on the purchase.