What do you mean by "cross country trips"?

If you are going to drive through washes and canyons, I'd
skip the X. If you are noogying across some flat grassy fields
and soft inclines with good footing, it should be no prob.

A 2nd set of beater wheels and 18" tires will do wonders...
I'd skip the tire joint store trip: a $60 floor jack from Sears,
a decent lug wrench and a torque wrench, and 30 mins of
wrassling wheels will give you a swap out.

I'd also consider a nice, used "under warranty" or CPO covered
4.6 or 4.8 or even 4.4, pre-2007, in lieu a new E70; someone else
has taken the depreciation hit and you won't be sweating as much on
driving a new, pristine E70 through the brush, imo.
GL,mD