Flashing a BIOS is not really useful if everything is stable. First, by fixing compatibility problem with newer hardware, it can cause problem with older hardware. So, if your hardware is stable and everything is recognized as it should, then that means that your BIOS is compatible with your current hardware.
Added feature are most of the time OC related. Higher voltage, higher FSB,... If your overclock seem limited by some value in the BIOS, then a newer BIOS might give you more options. Sometime, it update the BIOS for onboard IDE/RAID controller. You can update to the new BIOS if it add feature to the controller that can worth it.
While it was true some years ago that flashing a BIOS could increase performance, by now, the motherboard compagny has more experience with chipset that still run on the same standard (DDR memory that was harder to tweak at introduction time, but now very common and well know) so you cannot expect huge performance boost from flashing, unless running into some incompatibility problem that are easily identifiable. So if your computer feels fast, then probably it is the fastest it can go stock.
I still use the same BIOS that was on my motherboard when I first got it. Everything is stable. And the only reason that would make me update would be a new CPU core.
OTOH, flashing is a fairly secure operation now and if you feel the need, or have the confidence to do it and able to deals with the problems that would arise if something goes wrong, then it is up to you. I once flashed every revision that the manuf. would put on its web site, just for fun.. Until one time, my RAID array would not berecognized and my memory could not be ran as fast as the older revision.. and added to that, some posting problem...
From that time, I use the "if it aint broken, why fix it" method ..
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