Our 35d has 165000+ as well and has been a great vehicle. Just started throwing a 4d16 CEL code which, from what I've read, can have a number of causes. Other than that, runs/drives great after rebuilding the front suspension. We use it as the family daily and are averaging 13-14k/yr.

Also have the e53 1st gen x5. Love it as well, but for different reasons. E70 is much more refined, e53 is much more fun. E53 looks better (subjective). Only drive the e53 about 3000 miles a year the last couple years. I think were I in your situ, I'd keep the two I'm familiar with assuming they are both paid off. Devil you know it's better than the devil you don't.

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2005 X5 4.4i Build 04/05 Maintenance/Build Log
Nav, Pano, Sport (Purchased 06/14 w/ 109,000 miles) (Sold 8/15 w/121,000 miles)

2006 X5 4.8is Build 11/05 Maintenance/Build Log
Nav, DSP, Pano, Running Boards, OEM Tow Hitch, Cold Weather Pckg (Purchased 08/15 w/ 90,500 miles)

2010 X5 35d Build 02/10
Nav, HiFi, 6 DVD, Sports Pckg, Cold Weather Pckg, HUD, CAS, Running Boards, Leather Dash, PDC, Pano (Purchased 03/17 w/ 136,120 miles)