Mark you cant have it both ways... you said "Looks are deceiving...Latest X3 isn't much smaller these days" and you said "X3 proportions look weird" and then you said "go for a used X5" (which is the same size as a new X3).
If you want a X5 get one but the X3 is not so different in size or shape to be worth worrying about. Purchase and running cost and engine size are much more significant.
BMW i3 (BEV) 2014. . Capparis White. . Park Assist, Comfort Access, Enhanced USB
BMW X3 (F25) xDrive20d SE 2012. . Alpine White. . Oyster Leather . . 8 Speed Servotronic. .RFTs. . Electric Seats
Canon 70D 500mm, 85mm, 40mm, 24mm
Sony QX10 & GoPro Hero 3