Quick troubleshooting of ESX and 10Gb Broadcom NeXtreme II negotiated only to 1Gb

I have just realized that my vmnic(s) in one DELL blade server M620 (let's call him BLADE1) is connected only at 1Gb speed even I have 10Gb NIC(s) connected to Force10 IOA blade module(s). It should be connected at 10Gb and another blade  (let's call him BLADE2) with the same config is really connected at 10Gb speed.

So quick troubleshooting ... we have to find where is the difference

Let's go step by step ...

1. NIC ports on ESX vSwitch in BLADE1 are configured to  use auto negotiation so no problem here
2. Ports on Force 10 IOA are also configured for auto negotiation and configuration is consistent across all ports in switch modules so that's not a problem.
3. ESX builds are the same on both blade servers.
4. What are NIC firmwares? On BLADE1 there is 7.2.14 and on BLADE2 7.6.15

Bingo!!! Let's upgrade NIC firmwares on BLADE1 and check if this was the root cause of the problem ...