When messages get bigger, IpcChannel Remoting gets slower

I'm evaluating various interprocess communication methods for a couple of .NET 2.0 processes residing on the same machine. Naturally, .Net Remoting is a candidate, and theoretically the fastest configuration should be IpcChannel (named pipes) + BinaryFormatter.

My benchmarks really do show that Remoting over IpcChannel could mostly be faster than TcpChannel, but IpcChannel shows a steep drop in throughput as messages get bigger (around 30 MB):

Message Size    30 MB       3 MB        300 KB      3 KB
Remoting / TCP  120 MB/s    115.4 MB/s  109.5 MB/s  13.7 MB/s
Remoting / IPC  55 MB/s     223.3 MB/s  218.5 MB/s  20.3 MB/s

Does anyone have any idea why, or any idea how to optimize performance of either channel? I do need to pass 30 MB BLOBs around, and would like to avoid having to deal with shared memory / memory mapped files. Also, I can't afford writing these to disk (much slower).

The following method was used for the benchmarks (called repeatedly, measured total time, divided total payload size by total time).

private byte[] _bytes = null;

public byte[] HelloWorld(long size)
{
    if (_bytes == null || _bytes.Length != size)
        _bytes = new byte[size];
    return _bytes;
}