35 on the back does not worry me,m its the 40 on the front as I have an Xi and need to keep those circles the same size all around

Well if your on stock suspension you shouldnt have any problems watsoever, stock Xi's are like 4x4s, plenty of gap in the wheel wells...

I just want to confirm that a Mich A/S 3 275/35/19 WILL fit ok on the back of my 2010 BMW 550i Sport?

my 550i
 

I have a 07 550i and I run 19 inch staggered wheels front a 02 7 series 245 35 19 fronts and 275 30 19 rear just fine and I used the same set on when I had my 04 530i. However I was going through 2 sets of rears to 1 set of fronts the I went to an indy shop and they aligned me different that bmw specs and I have had a problem since.. but now I wondering should I be running 275 35's in the rear. I see from the photos that the well is filled nicley. I was going to move up to 20's staggered is this a bad idea. My 550i is not a sport model and I was thinking about getting the eibach pro Kit and that FSD strut setup with sway bars from a M5 and M6. Can anyone shed some knowledge on this..

07 550i