Josh Paetzel says For the moment you can dismiss the alert.
What do you think he means by that, if not that it's OK to use driver version 21 with firmware version 20? And then there's this (admittedly, from a different thread):
The driver writer for Broadcom/Avago/LSI (Yes, Broadcom now owns Avago) has said that the P21 driver *is* compatible with P20 firmware (especially since P20 is the latest firmware out).
Hey, it's your system; do what you want with it. But it's kind of odd to see a conversation go like this:
Josh: It's OK to do it.
You: OK, I won't do it.
@wblock: Really, it's OK to do it.
You: Fine, then I won't do it.
Cyberjock: We've confirmed that it's safe to do it.
You: That's why I won't do it.