Should I buy the MSD Street Fire 5520 or the 6AL for my street car (e.g. classic Mini)?

For street and everyday use, the 5520. Both have the same main functions (including a rev limiter). The 6AL has a bit more energy and is designed for track use (e.g. running on the limiter for a long time); for a street Mini it is money wasted. A proven Mini setup is: MSD 8222 coil + 5520 box + race-tailored MSD spark plug wires. For launch control, choose the 6AL-2.