Here's the latest review of the i8 with plenty of good info on the cars stats:
http://www.autocar.co.uk/car-review/...t-drive-review
What I find interesting is how close the i8 and M4 are in stats.
i8 wheelbase is 0.4" shorter than M4
i8 length is 2" longer than M4
i8 width is 4.6" wider than M4
i8 height is probably 2.5" lower than M4
i8 weight probably within 50 lbs of M4
i8 power 357hp 420 lb/ft vs M4 probably 450hp 415 lb/ft
First, I think this strongly supports the notion that the M4 weight will be close to 3300 lbs. According to the article above, the i8 achieves most of its weight savings from the same things Dr. Nitschke mentioned the M4 will utilize:
"The outer body is a combination of carbonfibre (roof), aluminium (bonnet and outer door panels) and composite plastic (bumpers, fenders)"
The i8 is a slightly larger car to the M4 overall and must support significantly more weight in the added complex componentry used for electrification including batteries and yet it still comes in at 3278 lbs.
The article indicates that BMW sees the Porsche 991 Carrera 4S as the direct conventional competition. However, the C4S is a significantly smaller car. I really think as far as conventional engined sports cars, the M4 appears to be the most direct competition to the i8. And unless green credentials are very important to the Buyer, a direct car to car comparison - i think the M4 has the advantage - with a bonus 40% discount.