I have a 4.10lsd in the 325ti right now, can cruise at 5k around 80 on the highway and get 30mpg with ease. Drove to new hamsphire, maine, vermont, new york, pennsylvania, and across ohio like this. 400 per tank without a problem and have proof of it. If you have a decent exhaust, that isnt loud for the hell of it, then these rpms are fine. The engines operate just fine at these speeds. Think of the ratios the euro gang have stock in their cars not to mention the roads, its easy for these engines to operate amazingly at these speeds and rpms.