You got those off an E38, correct?
E34 front M-Par is an 18x8 ET20. The E38 M-Par 18x9.5 is ET25. So you've got 1.5 inches of width total extra. As the E38 rim sits 5mm farther inboard you'll have 9/16ths of an inch extra on the outboard side, and 15/16ths of an inch extra on the inboard side. Now I don't know anyone that's tried it, but at almost an inch of extra wheel on the inside you're almost guaranteed for it to hit the shocks. And you might have to roll the fender to get the 9/16ths extra width to clear the outboard side.
Why would you even want to run 9.5's on all 4 corners if you've only got 2 of them anyways? This is assuming you've got a staggered E38 set which has 18x8's on the front.
Stock fitment on E34's for M-Pars is 245/40/18 on all 4 even though the wheel is 18x8 front and 18x9 rear. And you won't need wider rubber anyways with your 535 as long as you're using halfway decent rubber.
Just stick with the 18x8 on the front, and the 18x9.5 on the rear. Not only will you not have fitment issues then, but it'll ride & handle better without the extra mass & width of wheel the 9.5 has over the 8.
Cosmos Black/Black 1995 540iA M-Sport
BMW Individual Exclusive Edition, 1 of 65 total, 9/25/95 Build