Bit Error Rate Testing?

I have been experimenting with the gmsk demodulation block, and am able
to
successfully demod 50M+ continuous pseudorandom symbols at 2.0 MSym/sec.
Kudos to the USRP + GNURadio devs for making that possible, and thanks
for
making GNU Radio open-source.

The testing methodology so far has been to output the demodulator to a
file
sink, eg:

self.gmsk_demod = gmsk_demod(self, samples_per_symbol=2, verbose=True,
log=False)
limiter = gr.head(gr.sizeof_char, 10000000)
dst = gr.file_sink(1, ‘output.dat’)
self.connect(self.u, self.gmsk_demod, limiter, dst)

then to read the file into matlab and cross-correlate against the known
bit
sequence.

However, the time has come to start doing some bit error rate tests at
various SNRs, and the previously mentioned methodology starts to become
impractical for low BERs (given that you generally want to wait until
you
get 100-1000 or so errors).

SO: is there any way to get the demodulator’s output out to a pin
without
seriously harming the current performance of the demodulator? I have a
2nd
USRP available
if that opens up additional options.

Thanks for any advice.

-Steven