Whether it's noticeable or not, I would never put less than 91 octane or gas from any station other than Shell or Chevron. That dude sounds like a cheap bastard and his M3 should be revoked.
2008 E92 M3 6MT, AW/Blk Ext., brushed aluminum
2006 E46 M3 ZCP 6MT Carbon blk/blk(sold)
2001 E46 325Xi 5MT Jet Blk/Blk (sold)