4.5MB/s is expected on wireless N in the 2.4GHz range. In the 5GHz range you should be getting roughly double that in practice, so about 8 or 9MB/s.
Using N in the 2.4GHz range requires a large part of the 2.4GHz spectrum - the channel overlap is large, and if there is any inteference at all, then the rates drop quickly. The 5GHz spectrum has more available bandwidth, but also doesn’t pass through obstacles as effectively as signals in the 2.4GHz spectrum. So you’ll get less usable range in the 5GHz band.
If you run a wire, you can get around 20-30MB/s sustained on a gigabit ethernet network to the MBL.