Metrics of WarOf course, there is no real metric. That said, I believe the most useful one is "attacks/day." In September of 2005, the number of attacks by the opposition rose to 2,700, surpassing the previous high of roughly 2387. According to the Brookings Institution's Iraq Index, PDF page 20. This document changes a lot, so I am reprinting the graphic here, without permission. Footnote 37 reads
Alexandra Zavis, "Iraqi Insurgents Unleash Deadly Bombings, Attacks Despite U.S. Offensive," Associated Press, May 11, 2005.(Ed: retypeset for clarity)
Paul Garwood, "Surge in U.S. Troop Deaths Raises Concerns That Insurgents Retargeting," Associated Press, May 24, 2005.
Carol Williams, " Soldiers Get Extra Layer of Defense; Humvee crews are still not out of danger, but new protective plating provides a little more security on the hostile roadways of Iraq," Los Angeles Times, July 29, 2005.
Richard Oppel Jr., Eric Schmitt, and Thom Shanker, "Baghdad Bombings Raise New Questions About US Strategy in Iraq," New York Times, September 17, 2005. 65 to 75 attacks per day.
Bradley Graham, "Zarqawi `Hijacked' Insurgency; US General Says Foreign Fighters Now Seen as Main Threat," Washington Post, September 28, 2005. 90 attacks per day.
The Iraq Index, same issue, says tht the total number of killed or captured insurgents is over 50,000. There has never been an estimate that there were more than 20,000. The military, apparently, hasn't released a new estimate lately, it was "between 15 and 20,000" iirc.