I think that $40K is a fair offer. I think you should get the latest M3 with the V8 (perhaps a real good used one one where you can make a great deal right now at a dealership), if you do that then at least you have the following advantages ...
A) you experienced a longer arrangement with an M3 V8 other then test driving the car.
B) once the M4 is out and a year or so on the road and you learned if there are any issues or recalls ... then test drive the new M4 and decide on
Keep the M3 V8 or switch to a M4 6 with turbo ...
My two cents (Canadian
) ... good luck !
BTW ... I so agree with jdogg2000
... I would never pick up a first production year again from BMW I did on the sDrive Z4 35i 2009 and got burned badly by both rear wheels cracking on me during a cross country drive (Ontario to California and back). It was very disappointing the way BMW handled that issue on the 296 wheels on that Z4 (wheels cracked on many other Z4's and now have been redesigned stronger). So stay clear of first production year. My Z4 disappointment got me back into the M3 ... lets not talk about how many dollars I wasted
on e46 to a e89 and back to e92.