Is there a particular reason why you decided to purchase 14 physical servers instead of spinning up virtual instances (or even co-located servers) for easy scaling? As you've discovered, it's hard to estimate what kind of load you'll need to handle, and the up-front cost is impossible to recover.

Also, I'd recommend spending some time looking at your architecture, as you should be able to handle 50,000 active users with a lot less metal. The extra infrastructure can often be more expensive than a well-designed architecture.