Concurrent transactions

Given that the GSN-aware contract accepts only from the forwarder, how does setting the nonce for this forwarder contract work in the relay hub? I am asking because let’s say there are several hundred concurrent transactions being made to the same GSN-aware contract, it occurs to me that only the forwarder contract’s nonce matters? Is that thinking correct?

Also, has anyone tried (say on polygon) performance benchmarking, i.e. measure TPS per contract/relay server?