Newly purchased 3.0 E53, GM A5S390R Trans fluid change

[NZBM]

Just bought a 2003 X5, great car- very impressed with it so far after a 1100 KM drive to get it home over two days!
After looking for a new ski wagon to replace an old Subaru, I decided to go for a 3.0 petrol E53 which I'd wanted for some time, to add to my E46 collection! (330ci & 325i Wagon which we've had both for 5 years)

The X5 has 200,000 K's (approx. 120,000 Miles)
I'm currently going through it now with the usual PM's- CCV, Cooling system, valve cover & OFHG, drivetrain fluids etc. All of which I've previously done on both my E46's.

I've changed the trans fluid on both my E46's with ZF trans at much lower mileages with approx. 12 litres of Valvoline Max Life & genuine filter kits- 3X drain and fills, methodically topping of the fluid-correct procedure & temp etc. No issues.

I'm a little hesitant to just dive in and get it done on the X5 due to the miles and no evidence its been done previous. The trans performs flawlessly at the moment, but I want that old fluid gone!

I'm weighing up two options-

New filter kit & 3X drain/fills, getting 90% fluid change and little cross contamination of original semi synth vs Full synth Valvoline max life (which I find is a great trans fluid!)

OR

New filter kit with 1X drain and fill, then introduce X2 more staggered drain and fills later on (to prevent shocking it with all new fluid)

I much prefer the first option, but have read about many high mileage X5 trans dying shortly after a fluid change- although I believe this is due to incorrect top off/temp procedure, cheap rubber pan gasket leaking shortly afterward or using a flush machine?

This is not a "should I change my fluid ...but the label says lifetime etc" thread.
Just after some opinions on them two options from enthusiasts with real world experiences with a trans at approx. 120,000+ miles.

Cheers