Need recommendation

Hello, I'm fairly new to linode and had great success trasitioning our websites over. We run air shows and, for the most part, the web traffic is very low except during the shows where traffic increases 10 fold. For example, for the last show, we might have averaged 40 people on the site at once leading up the the show, but when the jets started flying we peaked at over 400 active users at once. Our primary linode is a 1024, so for the show I added a second linode and used a nodebalancer. This worked fine and I kind of think we couldv'e gotten by without it. But this was in a small city. My real question is what happens when we do a show in NYC and say 20,000 users hit the site at once. What should I do to prepare for that? Is it better to load balance multiple smaller linodes or should I just add one big linode? Is the load capability linear as you go up? Any help would be appreciated. Thanks.