The article is the May 2008 issue of Fly Fisherman Magazine, page 12. The author, Tom Keelin, measured 102 fish (mainly steelhead), and came up with the formula: weight=length x girth(squared)/690.
There is another snippet in the September 2008 issue of a giant brown that is estimated at 41.66 lbs using the above formula. In that same article it states that the IGFA all-tackle record brown trout is 40lb 4oz.
Comparing the fish in this post to the photo in the the September 2008 article, I'd venture a guess that this fish weighs closer to 40lbs, rather than the 25-30 mentioned earlier.
Either way, that's an awesome fish and maybe I'll be that lucky why I hit the Caney in a couple hours!
"I wish I was fishin'..." -me