I will answer. BMW has a premium for their horsepower as you have noticed. Drive the two with the same trans (auto or manual) and see what will be suitable for your needs. Know this though. The one that costs the most will sway you with "some" power increase. In '96 I went for the 328is (coupe was "is" then not "ic") over the 4 cyl. 318is because there were quite a few differences between the two besides cubic inches. When the 323 engine appeared BMW shot itself in the foot (briefly though) on their choice 323 vs 328. They were so close except for PRICE. They quickly played the nickel-dime game with horsepower and introduced the 325 and dropped cruise control, etc, etc, and al la carte items that once were standard. The DM dropped in value drastically against the $ but we saw no let up in price. Voila! more profit and movie coverage advertising! Now that there are two 6 cyl engines I would probably go with the lesser and get some options that are useful. After all, if your commute is anything like mine it won't make much difference anyway.
P.S. BMW may have added cruise control back on the car as standard but they did have it as an option in 2001 on the 325. Rear seat fold-down is standard on coupe and $495 on the sedan. Etc., etc a la carte!