Chris, I have absolutely no doubts in hardware handling this much of traffic without coughing, as you mentioned 42000 concurrent, here I assume 42000 users logged in at same time, so concurrent actually means how many of those CLICK at the same time, which of course wont be 42000 clicks in any given instance. You are running 3 load balanced nodes each with 32 GB RAM, so each server can easy handle 600-700 concurrent users (means clicks at any given instance) so all together 2100 is a LOT.
One thing you want to make sure, where you mentioned database servers, make sure you are putting SSD Drives on your databases, as its DB servers that takes most of punishment in any modern web application, and where IOPS are crucial, I always recommend SSD, just to give example an IDE drive 7200 RPM on RAID-1 gives IOPS of 240-260, whilst on same RAID configuration, a SSD gives out 30000-60000 (depending upon drive type and manufacturer), and where databases are just text files and hardly takes on too much space, it makes sense using SSD's, or even of you want to keep them on one server (web + database), then separate the drives for database within the server.
Finally, its always down to finding a sweet spot in HARDWARE, and then optimizing the software running on it. Ideally wait for sometime for more inputs from forum members (specifically Tim Hunt and Howard) as Tim is maintaining OU's web servers (8 web servers with 2 database servers in Master-Slave configuration) and OU can take on 50,000 users in a day.