Tire Help Needed! 2001 X5 4.4i Staggered fit

[FAT_X5]

Hello,
98K miles
I need some help. My x5 has the staggered fitment with 19's all the way around, and 255-50-19's in the front and I don't know what in the rear (I can't look because it's in the shop). I do know they are way wider in the rear.
I have bad ball joints and control arms and it made the front of my X pidgeon toed. Now the edge of each front tire, inside I think) is down to cord almost belt.
My quesiton is this:
Will 255-55-19's fit all the way around? I have some used Pirelli's (Zero)from my Range Rover Sport. How much wider is the wheel in the back of my X? Will these tires mess with the all wheel drive? Even though I only need new fronts, the shop says I must match the tread and brand to the rear otherwise I am asking for trouble.

If anyone has changed from staggered to standard or hear of someone who has, please let me know.


p.s.
The reason I took the X in was because it was running rough, and a check engine light. Come to find out, the purge valve was stuck open causing misfires, and there was no oil on the dipstick. I bought this thing 1 year ago and have put about 3K miles on it. The guy said it hadn't been serviced in years. Add a $600 100K mile service and the purge valve and suspension problems and I am $2K without the two tires I need..
DP