Honesty, I have an all malt American lager that I bittered to 16 IBU and it's way more bitter than coors orig. My cream ale gets 12-14 IBU and it's a lot more bitter than coors orig. If I were to try and clone it, I think I'd shoot for somewhere in the 6-10 range, starting at about 8. In a beer this light I find a couple IBU's very detectable.