On my system it is not that slow, and I think there are other users who use it without this problem, from the comments/usage statistics. So I'd like to keep it here and try to improve it.
I am aware of a problem that may cause this: when a download is created, the storage space is pre-allocated. During the time the blank file is created on the disk, the download cannot proceed. This will be fixed, but it will need some work and time.