Morning Phil
X3/X5 are very similar apart from engines the X3 have 2.0, 2.5 and 3.0 engine in both flavours Petrol and Diesel the latest models even have hybrid tech. X5 3.0 in both flavours and V8 petrol 4.4 to 4.8 My opinion is that the Achilles heel for all modern engines are the extended service periods that all manufactures tout, so my advice is oil changes annually or every 5k in my case to protect.
Modern Diesels also have DPF/EGR issues if short journeys are the norm, a good charge on a motorway once a month helps I am told . Tyres are the nemesis for all 4x4 if there is a difference in rolling radius front to rear the transfer box can be damaged so when replacing tyres I try to ensure I change all 4.
Off road our cars are not hardcore off road warriors (even the Land Rover boys beef stuff up and buy special tyres) but driven sensibly are OK I pop the box in manual select 3rd and let the torque work. Slippery grass fields and snotty gateways towing the horse trailer no problems, While out shooting muddy farm tracks and more slippery gateways (have you noticed farmers always put the gate in the muddiest corner of the field?) and not needed rescue yet.
I am on my 2nd X5 which originally we brought to tow a horse trailer after selling the Horse lorry in 2003. The first X5 was a 4.4 and I have to say faultless for 3 years then while out shooting a large tree blew over and squashed an Audi 2 pickups and the X5. I replaced it with the 4.6 X5 (now 156k) which has been an interesting learning process, but both cars have performed off the beaten track while towing at Horse shows and out on the shoots and never faltered. I was in Germany in 2007 and snow closed down a lot of areas but the X5 on winter tyres just kept going.
I have a friend who is a Landrover Discovery disciple he looked at the X5 and said "buy a good tow rope you will need it" Happy to report I have never been "towed" but have smugly towed him out off the sticky stuff twice 🤣
Bit of a ramble but I hope it helps
Dave