Opinion on X5 Towing

[pcognett]

I currently have a 2007 X3 (44K miles) that I am thinking about trading in for a new X5. A few questions for the folks on this board:

1) For 2011 model year, is the 5.0 or the Diesel better for towing? I love performance but solid all-year driving capability and safe towing are going to be more important than zooming 0-60.
2) The reason I need to tow is that I track my 2007 M6 and want to get an aluminum trailer to take to driving events. The M6 weighs in at 3909 lbs. and a decent trailer is likely going to be at least 2000 lbs. Is that amount of weight advisable or do I need to be thinking of some domestic pickup truck beast (not my preference)?
3) Does anyone have a sense of the cost for the dealer to install the trailer hitch, wiring, ball, etc.?
4) If I go the CPO route for an X5, would I need the 4.8 or the late model diesel?

Interested and appreicate any and all comments. The last thing I want to do is be driving down the highway and seeing my M6 besides my X5 if that is not a reasonable towing configuration.