Having been very successful with the router upgrade tonight, we are looking to move to the next router on Wednesday. Signs so far are that this should be equally seamless. We are, however, taking this slowly, one step at a time, to be sure.
We loaded 4 routers in all, and some were almost seamless, and some had a few seconds of outage, it was not perfect but way better than previously. We are now going to look in to the logs in detail and try to understand what we do next. Our goal here is zero packet loss for maintenance. I'd like to thank all those on irc for their useful feedback during these test.