What's the skinny on the M50? Have a mati 89 M20 I've put in tip-top shape, EAT chip and all (put in by former owner), and am eyeing a 91 525i and just want to know the pros and cons. Also, is it true I can get away with using the 91 and 93 octane fuels? Have been using 95 leaded, but someone told me I should be regularly using lower octane unleaded and just use the pricier stuff once in a while. Lastly, can I drop in my M20 EAT chip in the M50 If I choose to get it? If not, how much would an M50 chip cost?