First, 25 people is too small of a number to encompass the entire raiding team of a guild, 35-40 is more accurate. This being said, adding several modifications to the performance bar would be a boon to this service.
Firstly, marking pieces of gear as being the most outdated upon the bar would be useful, simply marking the piece of gear as it's icon in the general area where it is most suited would be good. Also placing an icon for gear that is on par with level, and one for gear that surpasses current expected level would be nice.
Now, for the addition of this performance bar for the guild audit, it would need to be handled differently. The colouration of the bar could remain the same, with it's divisions remaining unchanged. However, the option to toggle which character scores are averaged into the guild score would be needed, and then an option to see which characters detract from the average the most. Perhaps when mousing over the performance bar, if the mouse is over the green section, it shows which characters are still performing in the range of those instances, yellow which are on par, and red which are above average performance. Instead of having the icons next to the character names this is. A replacement for those would be a brief summarization of anything subpar (lacking/ unoptimal enchants, low-level gear). The option to expand characters for a complete overview from this abridged version would be a decent request also, in the form of maximizing/minimizing sub-windows to the whole system.
I apologize for the large amount of text presented here, and how it isn't so much abridged into a list.