I have one or two boards as well that has that option in the BIOS.
To quote what Gigabyte responded to about the Top Performance option in a review of their GA-7VAXP motherboard:
"Essentially, Top Performance optimizes the memory controller in the North Bridge for the best performance possible but at a stable enough state. So enabling Top Performance doesn't change any memory or frequency settings, it simply speeds up the internal timings of the memory controller."
However, do not be surprised if your suddenly get "blue screens" or intermittent crashes. On some motherboards (that I've worked with), it can lead to instability.
On my GA-7VAX motherboard (which is very similar to the board in the above mentioned review), I never had a problem with the Top Performance option enabled and there was a noticeable performance improvement as well.
I guess it comes down to the individual configuration you have (more likely, what type and brand of memory is installed).
PS: If the BIOS doesn't display the Advanced Chipset Features option, try holding in the CTRL key and pressing F1. That should bring up the option.
