Now kommts, one can dispense with the DD-WRT (as in my case, as only used as a wireless AP) and you play the Buffalo User Friendly firmware on it (the old and the new 1.85) goes in the part the Lutzie from.
With Buffalo 1.85 I mim Tablet 5 MB / sec and mim Labtop (connects only with 130 Mbit) as 6 to 8 Mb / sec at 7 to 8 meters distance.
At 8 meters distance and 1 wall + reinforced concrete ceiling, there are also still almost 8 Mb / sec. What is a Top value.
The Buffalo WLI-UC-WLAN stick G450-EU the speed is even again by 1 to 1.5 Mb / sec. go up. So about 58 Mbit. With my labtop but only 49 mbit, but he also combines max. with 130 mbit which theoretically should just go with the right Wlangegenstelle to 450 Mbit.
So that part has a super range and goes perfect through walls with little braked speed, but only with the Buffalo firmware.
Why such a part is then ever shipped with the DDWRT is my Rätzel. Especially since the problems were indeed existed in the first Firmewareversion and still not resolved. This shows it is indeed the Buffalo firmware.
So with Baffolo firmware 4 stars with DDWRT 1 star.