Well, depends on what youre used to 
At my parents home we had only 350kpbs for years - so I was pretty excited when I saw that I’m surfing with 800kpbs now 
Btw, I’ve switched wifi adapters again (I knew there’s a reason why I have alot of them…). Now the Pi is using an Realtek Semiconductor Corp. RTL8191SU 802.11n adapter with an external antenna, which seems to help a bit. I’m now having all green dots in the AP list and its loading with 250-400kbps.
And I found out, that when changing the position of the adapter/antenna even a few centimeters matter a lot (120kbps vs. 370kbps). So, maybe I’m busy trying to find a got location for the rest of the day 
But thanks so far for your help