I would use the 91. I have run 87 in my 300E and noticed it ran poorer. It won't blow the car up if all you can find is 87 for a one time fill up.

When gas is at these prices--what's the difference?!? Go for the 91...

-GH

__________________
For Now:
1992 Mercedes Benz 500SL
1998 BMW 528i
2003 Honda Element
2002 CBR600F4i
1977 Coachmen Motor Home