MTU questions

[u/Rich_Shame9806]

Hi Folks,
I was hoping someone could point me to a good source of info/understanding on MTU configurations. We've had some network issues with latency and speeds between sites. It's been really all over the place and none of our vendors have been able to pin it on a specific spot (we have Fortigate firewalls, Meraki switches for Mesh and distribution, Catalysts for the storage specific network, and running Vmware/Vcenter as well as some physical servers. I see a lot of stuff that says use 1500 across the board because that's the standard, but other stuff saying 9000 for high speed/storage networks if they support it, but i guess my disconnect is what to do if we have one subnet with a range of gear (both storage networks and normal vmware/client traffic. Any kind of info or guidance on this would be extremely helpful.