Connectx-4 25Gbps speed issue

We have issue in connectx-4 25Gbps speed, its shows 25Gbps in Esxi but practically the throughput is not going more 10Gbps. We test with different scenarios. Please help.

You might check that other components of connection -cables/switch and switch’s port support higher speed and configured properly.
Connecting it directly to other host switch 25 Gbps or higher speed may narrow the issue to specific component.

Its already verified from cisco. Is firmware or drivers parameters effect speed of NIC?

What kind of test you are running?
I would suggest to use ib_read_bw/ib_write_bw, that is part of perftest package, inside VM and connects port to the other host to eliminate switch from the picture and also bypass the kernel.
Another test from VM, that must have linux installed and latest MOFED package, is to execute
run_perftest_loopback 1 2 ib_write_bw
and see what is the output. If it still showing around 10Gbps, there might be limitation in the hardware, that most likely will be a server. For example, PCI speed and width are not expected.
In any case, there are little details about your setup in your questions - exact card PSID, firmware version, ESXi version, what are the tests, cable P/N, etc.