I use 98 only because in my twincharged Golf i noticed that 95 used 0.5 -0.8 l/100km more fuel. Even non BP 98 would use slightly more fuel.
I conducted this test over a long period... so even though the 328i is a different engine, i cannot bring myself to use anything other than BP Ultimate.
Further, Anecdotally my black soot problem is worse using 7-eleven's 98.
http://www.f30post.com/forums/showthread.php?t=759618