How to delete massive document library without taking the server down?

Hi, I have a single sharepoint front end server that has about a 500GB content DB (I inherited this). There's a single document library that is over 400GB that has been deleted which went easy enough, but now its in the second stage recycle bin, and if I try to delete it, it just makes the site completely unresponsive to other requests and after hours will eventually time out and start working again, but the library never gets deleted and I can see the changes were rolled back on the SQL server by looking at the database free space. I've also tried disabling the second stage recycle bin, and the recycle bin altogether, with basically the same result. I just this morning tried to restore the content DB so I could have someone just manually delete a little of the content at a time, but even trying to restore it makes the sharepoint site completely unresponsive. I look at the CPU utilization of both the sharepoint FE and the SQL server while performing any of these, and neither one seems to be doing much.

I've also tried with no success some powershell scripts I found etc. The server is 2012 R2 with Sharepoint Enterprise 2010. Any suggestions? Based on the free space in the DB the furthest it got was about 140GB before it quit and rolled back changes (it was down all saturday). It seems like if I could make it actually use the hardware somehow it could get it done but like I said it shows very little resource utilization when these are running so i'm not sure whats going on.