When you say the 540 is a "stripped" M5, how stripped is it? And is there a comparable version of the M6?

The 540 is basically an M5 with the 4.4L V8 rather than the 5L V10 in the M5. The M5 pulls about 500BHP, whereas the 540 doesn't. Equipment levels are comparable, which is why the M5 and M6 are such amazing cars; they're luxury saloons that really, really move.

M cars are also wallet-shatteringly expensive when they break, which is why people regularly cough up \ufffd1100 a year for the extended warranty.