A few things I've noticed since driving both vehicles:
1. The E53 feels lighter and the acceleration easier and faster during street driving. The E70 feels a bit heavier and slower, but that might be because I have a right front ride height sensor error that's wrecking havoc on the EDC system.
2. The E70 is much quieter and smoother on the highway. It also gets up to 85~100 with greater ease. Quiet and smooth is the impression on the E70. Where as the E53 is a bit noisier, the exhaust is somehow louder.
3. The exhaust sound on the E70 is simply awesome! A proper M engine sure sounds better than the alpina-inspired M62.
4. Much more creature comforts on the E70. Backup camera, side camera, Bluetooth music streaming, hard drive based navigation, better sound system, HUD, comfort access, the list goes on.
It'll take me some time to properly sort out the E70, even though it drives great as is. Just a few little things to work on before it is perfect.
Any thoughts?