Performance limit

It looks like i have reached a performance limit of MT. Starting with the last entry commenting is incredible slow. The cause is neither the perl version, nor the Blacklist nor the nofollow plugin. Attaching to the perl process with truss(1) I see endless pread(2) calls on the Berkeley DB files.
Anyone got an idea, how to improve performance?
Now I could setup a MySQL database, but I doubt that would be faster, and there are many larger Blogs that use Berkeley DB.
Or it may be time to say good bye to MT and switch to something else.
Unfortunately there not many advanced systems that use neither PHP nor a seperate Database Server.
This sucks!