Hi Robert,
I have a 525d auto with the 2.5l engine not the later 3.0l. The car being auto and an estate weighs in at, according to BMWf 1760Kg. I tow a sterling elite trekker weighing in at 1730 kg if fully loaded. I understand the 85% tow rule but also the law my ability and experiece and implications when towing at nearly 100%. But to help you with info the 5 series in my opinion is a very good tow car. The high torque of 400lb ensures swift, safe smooth acceleration when pulling off. With the added features of the dynamic stability control, abs and traction control I can only praise the car. Even to the extent on pulling the van off a wet uphill grass pitch last August where front wheel drive cars just gave up.
If you are nearer the recommended 85% tow limit and given the extra pulling power of the 3.0l you'll enjoy towing. You'll also have the advantage of smooth acceleration should you need to overtake coupled with BMW's great brakes when you need to stop.
In my opinion though pricey BMW's make great tow cars. There's a lot of people out there that will call me a plonker for this, I forgot to reduce my tyre pressure after a holiday and got through the rear tyres in 500 miles. I appreciate the safety implications but at