All of those counters look great to me too. Dell Networking switches implement receive flow control only. They never issue a flow control PAUSE frame when congested, but do respect received flow control PAUSE frames received from other switches. So I could see this being an issue only if the switch was receiving pause frames, which it does not look like it is. a packet capture may be the way to go. This would give more details on the types of packets being discarded. use WireShark to analyze the capture and inspect the discarded packets.  The firmware being run is a bit outdated, If you have some downtime you could schedule for an update. I would update to 6.2.6.7 for now. That release is pretty stable. [URL] There is also supposed to be a new 6.3 firmware release in the works, hopefully we see it within the next couple weeks. Having the firmware up to date can help with overall operability, and may help the switch process those packets.  You mentioned previous a theory of the interface being saturated. Do you have any additional interface on the switch/server? You could setup a LAG and see if that helps alleviate some of the issues being seen.
That's not a huge amount of discards given how long the port has been up but its still indicating some network congestion.  I've noticed this on several trunks and was wondering if anyone thought it excessive?   Thanks for any comments! 
6544 transmit Discards - N4032