@Morten: sorry, I completely missed your earlier posts about M.Greve's setup, I apologize (lazy me!! ). From the picture you posted I noticed some changes.
First, he now uses a Schulze ESC which in his words provides better performance in mid-range and on startup (main problem with outrunner-type motors). Still not perfect, though: on one flight he got ther motor running backwards for a short period. I guess some work is still to be done.
Secondly, he replaced the heavy receiver NiCd-battery with Lipos soldered directly to the 10S3P pack. This brings more security as the aren't charged inside the plane where they can eventually catch fire and burn.
Last, the added weight of the floats must be about 350g, maybe less since his are really light and small. In the air the float act like a brake and further slows the plane down. What he showed and what impressed the most of us was how slow the whole setup was flying but still how much power to pull the aircraft vertical without problems and very quietly (you only hear the propeller).
He also told me that they are trying to put together a package everyone can buy which includes engine, lipos, ESC, chargers and all the hardware; pilots should then be able to buy a unit that works and that can effortlessly be installed in a 2m pattern plane. More about this in the coming months.

Regards,
-Fabrizio