New tubes in Rogue M-180 Monoblocks

I understand the M-180s now ship with the KT-120 power tubes, instead of the KT-80. You can also simply replace the KT-80 with the KT-120 if you already own these amps. I'm curious whether anyone has done it and what their impressions are as far as the difference in sound. Is the over $300 upgrade worth it?