Thanks for that guys.
I really wanted some caravan towing info as well though. We changed our caravan earlier this year and have found that my 535 is not so happy with it. Power wise the BMW is more than up for it, but we had a bit of a 'tank slapper' coming back from a short break recently. Admittedly I was doing nearly 70 (but the van was not overloaded etc etc) but it did shake me up a bit.
We are not contemplating buying the rx400 just for towing, it will probably only be used four or five times a year for shortish runs with the van, but the other issues of reasonable performance with 'reasonable' economy, a lovely relaxing drive and loads of extras thrown in for good measure.
Like I said before, our local (?) dealer was more than helpfull and offerd us the extended test drive. We only went into the dealers because my wife liked the look of it and we were window shoppingso to speak.