Hoo boy, 9% gain* for 40% more gas. So what happens to the WonderJet's radius of action when I start loading the pylons with stuff that adds weight and drag and doesn't make the engine go, because I might want to carry more ordnance than an A-29? I'll take "down the *****er" for $20, Pat!
And from what you say, it's not so much that they haven't been tested as that they don't do anything useful.
*surely you mean "performance" rather than "fuel", 'cos I'm not guessing when I calculate 950 USG of drop tank gas relative to 13 klb internal.