Yes, there are tons of people using FreePBX/Asterisk for their call center(s)
For the size you mentioned, you’ll definitely need some commercial and third party modules, such as Queue Callback, Queue Reports, Queue Dashboard and likely CRM integration.
FreePBX offers a commercial version of the queue module which gives you additional features, such as virtual queues etc.
See Wiki: https://wiki.freepbx.org/pages/viewpage.action?pageId=8421516
FreePBX also offers a commercial Queue Callback module, See Wiki: https://wiki.freepbx.org/display/FPG/Queue+Callback+Module
CRM integration module: https://wiki.freepbx.org/display/FPG/Sangoma+CRM+REST+API
To be honest, Queues Pro and CRM module, we never really used it so I cannot provide any feedback on that.
(Queues Pro we used once to send post queue calls to a survey, CRM we did the integration on our own)
The Queue Callback module we had some real trouble with high call volume and we went through hell with support. But for the past year or so it appears to be stable tho.
Unfortunately, FreePBX does not have yet a good Queue Dashboard or queue reporting solution that beats Asternic.
Queue dashboard: fop2.com
Queue reporting: asternic.biz
The ups are, that Asterisk/FreePBX, if configured properly, can handle a ton of calls on little resources. Also, a lot of people are using Asterisk which means that you have a bigger community support, finally, you can easily integrate and build whatever application you want using ARI/AMI.
The downs, you’ll likely need to use third party and commercial applications, and like any CRITICAL software application you run in production. You either need to know it fairly well to be able to solve problems immediately, or have a good support contract.