One of my fondest moments in my car was racing a 911 C4S on the track. We headed around the final turn into the straight and I blew the Porsche away. Now, he did finally dummy me on the turns but straight line speed the C4S did not have a chance.
If you like twisties and status the Porsche is a no brainer. If you like the visceral feel of the power in a pretty agile machine than get the 135i. Either way you probably cannot go wrong. Have fun shopping!
2015 F82 M4 - YMB - DCT
2008 E90 335xi - N54 Daily Driver