This forum is effectively dead. I think this is the most recent post, but for what it's worth, and if you haven't gotten a response, it may be.
Do you have metrics for the interface on the server? Is it maxed out at 900+ mpbs? Does the server have an additional NIC that you can bond and see if it helps? Is the server still using mechanical disks or is it SSD or enterprise flash? Often, workstations don't need any more than a gig connection, but the server can benefit from it. Your switch may even already have an SFP+ slot that you can use.
Long story short, I wouldn't upgrade the whole environment to 10 gig, just the server, but I'd also look at the server itself to identify other potential bottlenecks like disk speed and access latency.
Chaos reigns within. Reflect, repent, and reboot. Order shall return.
Slivovitz owns you.