Concurrent reads on the ZipFile archive is terribly slow on multiprocessor systems. On my 4 CPU laptop it shows 26 reads/s vs 2 reads/s on 100MB samples for example.
The cause is the use of synchronized blocks to access the underlying file channel. This may be required for generic SeekableByteChannel but most commonly there is FileChannel implementation which supports lock-free reading from any position (i.e. using pread/pwrite system calls or their equivalent).
With the fix the performance is about 10 times faster (on 4 CPU system, with more processor the difference should grow significantly).