I assume you have had the boat and trailer on the scales, and have a real-world estimate of what the weight will be (with typical fuel and water loads, etc).

The 3.0 is rated to tow 6000 lbs from 2004 onwards, and the manual transmission was rated to tow 6000 lbs from 2001. The 3.0 automatic from 2001-2003 was rated to tow 5000 lbs. So, you are in the range. With a manual transmission, it has a stump-puller first gear, so that is in your favour and clutches shouldn't be an issue.

Not sure how wet/slippery/steep your launching ramps are, but the X5 is fairly sure-footed, so should be fine.

You are pretty much at the weight limit of towing for the 3.0, and need to consider the wind resistance as much as the weight. If you are on flat ground, and are comfortable towing that weight, the 3.0 will do fine, but it won't be racing up the on ramps.

One thought is whether the ramps are steep enough to get the boat floating without getting the back of the X5 wet. There isn't as much rear overhang on the X5 as many other vehicles, and that is very good for towing stability, but not so good for the reach required with some trailers.

Strongly recommend you only consider the OEM hitch, and OEM wiring kit.

If you do a search, there are lots of pictures/stories on here about towing large trailers and boats. I never towed over 5000 lbs with my 3.0 Steptronic, but it did fine.

Good luck, and let us know how it works out.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue