It depends. Median request size, number of keep-alive connections, filesystem cache hit ratio, NIC driver quality, and dirver/OS tuning parameters all matter a great deal. With the filesystem cache being the most important.
As good as nginx is, how fast it can send is limited by how fast it can read data. 10 Gbps is roughly 1 GByte/sec. If the data set is all coming from RAM cache, that's do-able. Otherwise, you're going to bottleneck at the storage layer (unless you have a several fast SSDs in a RAID configuration or a whole lot of spinning rust). Also note that you will need to run several nginx worker processes per core in order to avoid blocking on disk access under Linux because asynchronous IO in Linux is basically broken by design.